While it may not be mandatory, it is STRONGLY recommended to have a business lawyer make any agreements or contracts for your business. An experienced business lawyer will help ensure these agreements are written correctly, understandable, and most importantly… Protect you and your business.
This is generally referred to as breach of contract. If all parties agreed to the contract conditions and failed to uphold those conditions, they can be found in violation of the agreement and taken to court.
There is no law that states a contract must be written by a lawyer in order for it to be recognized legally; you can draft up a contract on the back of a pizza box if you wish. However, a lawyer will help make sure that drafted correctly and it protects you.