Tampering with evidence refers to what a person is charged with if they change or alter any piece of evidence in a court case. This includes destroying the evidence.
The charge is criminal in nature and will create a criminal conviction that normally includes jail time. If such a charge is leveled against either party in a court case, the other party will end up winning by default due to the other's intent to deceive the court.
In most instances, it is the defendant who is charged with tampering evidence, as they would be the one most likely to want to hide something that the court would consider a material fact.
Changing the date or an amount in a contract will also result in an evidence tampering charge.