Gov. Charlie Baker has vetoed a bill that would have allowed retired Boston police officers to serve on police details, writing in a letter to lawmakers that the legislation would have caused Massachusetts unemployment law to violate federal requirements.

The bill, a home rule petition filed by Rep. Daniel Hunt, sought to give the Boston police commissioner the power to appoint retired city police officers as special officers, enabling them to work details as needed. The original Boston City Council petition notes that the city cannot fill all its detail requests and the training and experience of retired officers could make them well-suited for the work.

In his letter to the House and Senate, Baker wrote that he supported the bill's aims and believed it would strengthen public safety in Boston, but said that the U.S. Department of Labor alerted his office that its passage as written could jeopardize the state's federal certification. Baker wrote that he would normally suggest an amendment, but returned the bill unsigned because the Legislature cannot amend home rule petitions. He urged lawmakers to favorably consider a revised version of the bill if the city puts one forward.