; (2) to coerce an employee into undertaking or promising not to pursue, bring, join, litigate, or support any kind of joint, class, or collective claim arising from or relating to the employment of such employee; or (3) to retaliate or threaten to retaliate against an employee for refusing to undertake or promise not to pursue, bring, join, litigate, or support any kind of joint, class, or collective claim arising from or relating to the employment of such employee: Provided , That any agreement that violates this subsection or results from a violation of this subsection shall be to such extent unenforceable and void: Provided further , That this subsection shall not apply to any agreement embodied in or expressly permitted by a contract between an employer and a labor organization. ; (6) in subsection (g), by striking clause (B) of the last sentence of section 8(d) of this Act and inserting subsection (d)(2)(B)