It shall be unlawful for any person to discharge, fine, suspend, expel, discipline, or discriminate against a participant or beneficiary for exercising any right to which he is entitled under the provisions of an employee benefit plan, this subchapter, section 1201 of this title, or the Welfare and Pension Plans Disclosure Act [29 U.S.C. 301 et seq.], or for the purpose of interfering with the attainment of any right to which such participant may become entitled under the plan, this subchapter, or the Welfare and Pension Plans Disclosure Act. It shall be unlawful for any person to discharge, fine, suspend, expel, or discriminate against any person because he has given information or has testified or is about to testify in any inquiry or proceeding relating to this chapter or the Welfare and Pension Plans Disclosure Act. In the case of a multiemployer plan, it shall be unlawful for the plan sponsor or any other person to discriminate against any contributing employer for exercising rights under this chapter or for giving information or testifying in any inquiry or proceeding relating to this chapter before Congress. The provisions of section 1132 of this title shall be applicable in the enforcement of this section.