It would not be a valid contract. A contract to break the law is illegal.
Fraud invalidates a contact because law requires it.
It depends on what law is violated and what type of violation.
Contract law.
Contract law
Yes. Federal law, state law and even municipal law prevail over negotiated contracts. A contract that requires one party to violate the law (e.g. a contract for an assassination), or relies on a concept invalidated by law (e.g. a contract for the sale of a slave) is unenforceable. Any law suit for breach of such a contract would be dismissed as soon as the violation of the applicable law was demonstrated. This is common to all jurisdictions based on British common law.
Only if they've broken a law that requires jail time. Otherwise, no.
No. Not unless you have a specific union or employment contract that requires something different.
Contractual Law. The non-payment is a breach of contract
Private laws are those that do not apply to everyone. An example of private law is a contract. As long as it is not illegal, you can contract for many things or you contract away your rights.
Contract law is a large and complex area of the law. You can find a summary of the main principles of contract law by visiting the Wikipedia page titled English contract law.
Generally, the action would involve breach of contract.
Contract law is just a body of law regarding... well... contracts.