contract law is the body of precedent and collective set of laws related to the legality, construction, execution and all around use of contracts, and while I’m sure there are some specific extra laws that make breach of certain types of contracts a misdemeanour or felony. Generally speaking in most jurisdictions around the world in fact, breach of contract is a civil law matter between the parties of the contract, and settlement of the civil law side of the “is this actually a breach of contract” is usually necessary first before any potential criminal liability can be applied.
An example: An contract can be invalidated for lack of sufficient consideration offered (peppercorn isn’t always enough to make it valid)… this makes the contract void, not illegal. This is a simple example but it illustrates the basic point well, and I’m not trying to write a legal theory essay while on the way to work.