Mayors from across the country who are gathered in Boston this weekend for the US Conference of Mayors meeting announced a coalition in support of the state’s transgender antidiscrimination law, in advance of a November ballot question that would revoke it.

The Mayors Against LGBT Discrimination coalition includes 320 mayors and town managers nationally.

Massachusetts mayors who signed on include: Martin J. Walsh of Boston; Kim Driscoll of Salem; Daniel Rivera of Lawrence; Paul Heroux of Attleboro; Alex Morse of Holyoke; Robert Dolan of Melrose; Jon Mitchell of New Bedford; Ruthanne Fuller of Newton; David Narkewicz of Northampton; Linda Tyer of Pittsfield; Joseph Curtatone of Somerville; Domenic Sarno of Springfield; Marc McGovern of Cambridge; and Joseph Petty of Worcester.

“Supporting this law is simply the right thing to do,’’ Walsh said in a statement. “This law has been in place in Massachusetts for two years with no issues, and a similar local ordinance has been in place in Boston for more than a decade. In that time, we have become a more welcoming and inclusive city for our transgender friends and neighbors. We can’t take a step backwards.’’

Massachusetts is one of 19 states with nondiscrimination protections for transgender people in public places, including medical offices, restaurants, and shops, as well as public restrooms and locker rooms. New Hampshire just enacted its measure last week.

“The Mayors Against LGBT Discrimination coalition is committed to ensuring basic protections so that all people are treated fairly, no matter who they are or where they live,’’ the coalition said in a joint statement. “As mayors, we uniquely know the importance of moving forward to strengthen communities and provide a welcoming, safe environment for all neighbors and businesses, and we oppose any ballot measure that would take the state backwards by removing critical protections.’’

A group called Keep MA Safe petitioned for the ballot question asking voters if that law should remain or be revoked. The group has raised concerns about safety, given the mingling of people of different genders in public bathrooms.

The Mayors Against LGBT Coalition is cochaired by mayors Muriel Bowser of the District of Columbia, Jenny Durkan of Seattle, Sly James of Kansas City, Mo., and Jim Kenney of Philadelphia.

Stephanie Ebbert can be reached at Stephanie.Ebbert@globe.com. Follow her on Twitter @StephanieEbbert