Section 105A. No employer shall discriminate in any way in the payment of wages as between the sexes, or pay any person in his employ salary or wage rates less than the rates paid to employees of the opposite sex for work of like or comparable character or work on like or comparable operations; provided, however, that variations in rates of pay shall not be prohibited when based upon a difference in seniority. Any employer who violates any provision of this section shall be liable to the employee or employees affected in the amount of their unpaid wages, and in an additional equal amount of liquidated damages. Action to recover such liability may be maintained in any court of competent jurisdiction by any one or more employees for and in behalf of himself or themselves and other employees similarly situated and any agreement between the employer and any such employee to work for less than the wage to which such employee is entitled under this section shall be no defence to such action. The court in such action shall, in addition to any judgment awarded to the plaintiff or plaintiffs, allow a reasonable attorney's fee to be paid by the defendant, and the costs of the action. At the request of any employee paid less than the wage to which he is entitled under this section, the attorney general may take an assignment of such wage claim in trust for the assigning employee and may bring legal action necessary to collect such claim, and the employer shall be required to pay an additional equal amount of liquidated damages, together with the costs of the action and such reasonable attorney's fee as may be allowed by the court. The attorney general shall not be required to pay any filing fee, or other costs, in connection with such action. The commissioner may join various claimants against the employer in one cause of action. Any action based upon or arising under sections one hundred and five A to one hundred and five C, inclusive, shall be instituted within one year after the date of the alleged violation.