Contract laws generally prohibit contracts that restrain trade. Contracts restraining trade are defined as contracts that reduce the level of competition involved in the commercial exchange of goods or services. Contracts that restrain trade are considered a classification of contracts that are contrary to public policy.

These kinds of contracts are sometimes defined by contract laws as covenants not to compete and sometimes as non-competition contracts. Whichever they are known as, though, they are illegal and are thus considered unenforceable. 

Elements of contracts that restrain trade are generally permissible if they are limited in scope or duration. A contract is permissible if it compels a party to the contract to relinquish the right to make a particular thing, but not if it attempts to force one of the parties to the contract to not compete with the other in any way in the future.

Contracts are permitted to contain non-competition clauses if the clause exists in order to protect business secrets of the employer, or if the non-competition element of the contract seeks to limit a former employee from utilizing business contacts which are considered essential to the operations of the company with which the original contract was signed.

A contract may be ruled to be illegal by any court of law. Illegality can become an issue even if the normal requirements of acceptance of offers, consideration, contractual capacity, are present. Illegal contracts typically do not result in any liability for the involved parties. The courts may rule an illegal contract exists regardless of whether or not the parties involved in the suit raise the issue, even if the two parties believe the contract to be legal.

A severable or divisible contract may be formed by the parties to the contract or may result from actions of the courts. The parties can create a severable contract by including a severence clause into the original contract. A severance clause is a clause which states that if there is one other contractual clause that would cause the contract to be considered illegal, then the offending phrase should be stricken from the contract, so long as the removal of the clause does not substantially alter the original nature of the contract. 

Divisible contracts are similar contracts entered into by the same parties which have similar terms but can be completed independently of each other. A court may form a severable contract by utilizing a blue pencil test. If the offending phrase in a contract can be removed from the contract without enacting any change besides turning an illegal contract into a legal one, then the change passes the blue pencil test.

A contract can be challenged by one of the parties to the contract if they claim their assent was not genuine because they were subject to undue influence. Undue influence is said to exist if an inordinate amount of pressure is placed upon a party to enter into a contract against their best interests. Undue influence cannot be invoked by a party simply because they are in a detrimental contract. 

Undue influence is usually only claimed in the event that the party is in a relationship wherein another person is able to influence their decisions. Normally undue influence can only be successfully claimed by a minor or an elderly person who has a guardian responsible for overseeing their legal or financial obligations.

Other relationships in which undue influence may arise include attorney-client relationships, doctor-patient relationships, and the relationships between the beneficiaries of a trust and the individual responsible for managing the trust.

An occurrence of undue influence can be difficult to establish conclusively in court. There is sometimes an automatic presumption of undue influence by the courts. A presumption of undue influence can be established if the party in the superior position influenced the dependent party to agree to a contract that benefited the superior party.

If the dependent party challenges a party that they were influenced to create by their guardian, the courts are likely to issue a presumption of undue influence because they believe that if the contract did not arise due to undue influence, then the dependent would not be challenging the contract.

The guardian involved in a court case in which the genuineness of assent in a contractual dispute involves a presumption of undue influence often bears the responsibility of disproving the charge filed against them by their ward. The undue influence charge is often repudiated by presenting evidence that the ward inquired about the terms of the contract or was afforded the opportunity to consult with an independent party that did not have a direct stake in the contractual negotiations that are being challenged.

The guardian can disprove that there has been an occurrence of undue influence even if there was a benefit conveyed to the guardian if they can demonstrate that the ward received a full disclosure of the benefit that the guardian would derive from the contract. If the guardian can prove that full disclosure was presented to the ward, that the ward obtained independent analysis of the benefits that all involved parties would receive, then the presumption of undue influence can be disproven.

In the event that undue influence is found to have existed by the courts, the courts will declare the contract to be voidable by the ward. Undue influence, however, cannot be claimed by a ward that acted upon the innocent advice of their guardian yet was harmed by the contract in a way that did not benefit the guardian.

Fraudulent misrepresentation by silence may result during a long contract negotiation if one of the parties to the contract withholds material information they learned during the negotiation process.

As a legal concept, duress has a long tradition. Duress is related to the concept of undue influence. Duress exists when there is a threat of bodily harm, and the threat is immediate and cannot be avoided. Duress also exists in criminal law proceedings. In order for duress to exists in a contract law court proceeding there must be a wrongful or illegal threatened act. 

A contract also cannot normally be made voidable because one of the parties is suffering from economic duress. Claims of duress are filed by parties to a contract seeking to prove that their assent to a contract was not genuine, and thus did not fulfill the essential requirements needed to form a contract.

A contract cannot be invalidated by a party to that contract who claims duress because the other party threatened to sue them for a larger amount, because the filing of a law suit is a legally permitted action. A claim of duress is distinct from instances where the consideration offered by one of the parties is the forbearance of an action. 

Duress can be invoked if the party claiming they were acting under duress was in fear for their safety. An example of duress would be if a person is told to sign a contract or their family or they themselves would be harmed. This qualifies as duress because the consideration of forbearance is to forbear from doing an illegal act. If it is a wrongful or illegal threatened act then it constitutes an instance of duress.

A claim of economic duress is not usually permitted. Individuals are usually only able to successfully invoke a claim of economic duress if the other party in the contract is the immediate cause of the economic duress. Sometimes the courts permit a claim of economic duress to be filed in contracts which involve one party claims they are suffering from economic difficulties which are not caused by the other party in the contract, although such claims of economic duress are not usually accepted. 

Economic duress does not exist simply if exorbitant prices are charged for goods or a service. However, if the high prices are charged by the same party that created the need for the good or service then a claim of economic duress may be permitted by the courts.

If the individual claiming the contract was formed under duress is able to prove their claim, then the courts may declare the contract voidable. 

Non-fraudulent misrepresentation can take one of two forms: innocent misrepresentation or negligent misrepresentation. Negligent misrepresentation is considered in the eyes of the law to contain the same level of culpability as fraudulent misrepresentation.

Misrepresentation that is negligent in nature is treated by the courts in the same way as a fraudulent misrepresentation. Negligent misrepresentation occurs when a party to a contract does not carry out a reasonable effort to ensure that their claims as the material information at the heart of the contract are true.

If one of the parties to the contract in question does not act with the professionalism that would reasonably be expected from an individual in that position, and the other party relies on that professionalism when entering into the contract, then negligent misrepresentation may be determined by the courts to have happened.

Fraudulent misrepresentation may be claimed by a party attempting to have a contract declared void if three different criteria are met. The first is that there is an occurrence intended to create justifiable reliance on a fraudulent misrepresentation. 

The party seeking to have a contract invalidated must show that they entered into the contract due to a justifiable reliance on the other party’s fraudulent misrepresentation. Justifiable reliance only becomes an issue if the claim is not readily apparent to be false. Failure to investigate a claim may be used to support a claim of justifiable reliance. The material misrepresentation must be made about an area that the injured party had no way of proving and thus was forced to rely on the other party’s statement.