§ 23

The commissioner may participate jointly with the Secretary of the Treasury of the United States or his delegate, or with the proper tax officer of any territory, state or political subdivision thereof or with any agent or agency designated under the laws of any territory, state or political subdivision thereof in the examination, verification, assessment, audit or other activity to determine the proper tax liability due on any tax return required to be filed with him. The commissioner may participate jointly with said tax officers in the examination, verification, assessment, audit or other activity to determine the proper tax liability due on any tax return required to be filed with the Internal Revenue Service or with any territory, state or political subdivision thereof to the extent that the tax of the federal government or of the territory, state or political subdivision thereof is similar to a tax imposed by the commonwealth. A certificate by the commissioner that the tax of the federal government or of such other territory, state or political subdivision thereof is similar to a tax imposed by the commonwealth shall be prima facie evidence of such similarity.