The Houston Court of Appeals has found that the defense of illegality does not void a Mediated Settlement Agreement.  As background, any contract or agreement may be voided if it’s illegal.  You can’t for example enforce a contract to rob a bank.  In In re Marriage of Quinones, husband and wife signed a mediated settlement agreement resolving the issues of their divorce.  The husband rescinded claiming that because his wife was an “illegal alien” the agreement itself was illegal.  The Court of Appeals found that her immigration status had no effect on the enforceability of the agreement whether she was in the United States legally or not.