Undue influence is power over someone else which is used to push the weaker person into making a decision which would not otherwise have been made. A classic example of a situation in which undue influence might be used is in the drafting of a will. Someone could pressure the testator to include a legacy or gift which the testator had no intention of including originally, using a variety of manipulative tactics such as trickery, flattering, or suggestion.
Under the law, if it can be demonstrated that a contract, will, or other document was made in circumstances in which undue influence was involved, it can be set aside. In the case of a contract, for example, the person who was influenced will not be held to the contract. With documents like wills, family members may challenge the document in probate because they believe that it does not truly represent the intentions of the deceased.
Certain types of relationships are believed to be especially prone to undue influence by their nature, such as spousal relationships, parent/child relationships, doctor/patient relationships, and religious officiant/parishioner relationships. In other instances, the relationship between the two people is not necessarily one where this type of influence is presumed to be present, but evidence can be presented to show that it occurred.
Several things can point to the presence of undue influence in a transaction. The first is the existence of a transaction or agreement which appears odd and out of character. For example, if a woman donates to an opposition political party in her will, this might raise a red flag. Being in a position of vulnerability or susceptibility is another warning sign. In the example above, for instance, if the woman was elderly and heavily reliant on a caregiver in her home, this could mean that the caregiver had influenced her.
Next, there must be evidence of opportunity. If it can be shown that someone in a position to have undue influence had opportunities to use it, this can indicate that a questionable transaction may be the result of that influence. Finally, evidence is required. It can be tricky to muster evidence because people using manipulation in transactions tend to keep their activities quiet because they do not want to be caught.
This is not the same thing as duress. In duress and coercion, people are physically threatened or subjected to physical violence in order to achieve a desired outcome. Undue influence does not involve violence or threats of violence, relying on other manipulative techniques instead.