Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 29, § 61

The comptroller or any other person authorized to approve claims for materials, supplies or other articles furnished to, or for service or labor performed for, the commonwealth, may, before approving any such claim, require the claimant to certify on oath that all the articles have been furnished, for which the claim has been made, or that the service or labor has been performed, and that no commission, discount, bonus, present or reward of any kind has been received or promised or is expected on account of the same.