According to EU law, if a contract you sign is illegal ( as is a clause that forbids you to participate in free media), the employer is liable, not the employee.
It is the employer who must make sure any contract is according the law. The employee acts in good trust that the employer is adhering to all EU laws, which, by the way take priority over any local ( yes, also Irish) laws.
IF the employer would fire you for breach of an illegal clause in a contract, you have a win win at court as not only were you wrongfully dismissed, the employer is ALSO guilty of obliging people to sign an illegal contract. That is called protection of employees And legal liability of the employer.