Mayor Michelle Wu had a great Saturday: her bid for a second term was endorsed by five Service Employees International Union groups, representing 135,000 Massachusetts workers.

“SEIU members have a tradition of deep political engagement, and the unions’ endorsements bring with them hundreds of active volunteers who will help get out the vote and lift up key issues important to union members in the mayoral race,” the SEIU Massachusetts State Council press release states.

The five unions made their endorsement Saturday afternoon at the downtown Boston union hall of the 32BJ SEIU union, which says it’s the largest property service workers’ union in the country, boasting more than 175,000 members across 12 states, including 19,000 in Massachusetts and Rhode Island.

32BJ was joined by four other union groups: 1199SEIU United Healthcare Workers East, which has more than 85,000 members in the Bay State; SEIU 1957 CIR, which includes more than “20,000 medical interns, residents and fellows nationally”; SEIU Local 509, with “20,000 health, human service, and higher education workers”; and SEIU Local 888, with “8,000 workers in state and municipal services and higher education.”

The major endorsement follows that of the Boston Police Patrolman’s Association last month.

Wu’s bid is challenged by Josh Kraft, the son of billionaire New England Patriots owner Robert Kraft and former head of the family’s philanthropic efforts. If no one else declares, then the Sept. 9 primary is not required. The election is set for Nov. 4.