Section 20A. The provisions of this chapter shall not be applicable to any cause of action accruing more than 3 years prior to the date of filing in court of a criminal or civil action; provided, however, that the limitation period shall be tolled from the date that the employee or a similarly situated employee files a complaint with the attorney general alleging a violation of this chapter until the date that the attorney general issues a letter authorizing a private right of action or the date that an enforcement action by the attorney general becomes final.