Transgender rights activists say they will announce Monday that the New England Patriots, New England Revolution, Boston Celtics, Boston Bruins, and TD Garden are backing an antidiscrimination measure before the state Legislature.
The Boston Red Sox have already declared support for the bill, which would ban discrimination against transgender people in restaurants, shopping malls, and other public accommodations.
Advocates say backing from the world of sports, which has not traditionally been a bastion of support for gay, lesbian, bisexual, and transgender causes, demonstrates the increasingly mainstream appeal of their campaign.
“It shows that this is not a controversial issue,” said Carly Burton, campaign manager for Freedom Massachusetts, a coalition of advocacy groups, businesses, and elected officials pressing for the legislation. “A wide variety of people, a wide variety of businesses, support nondiscrimination protections.”
But advocates, however broad their coalition, have been unable to get the bill through the Legislature so far.
The left-leaning state Senate is expected to pass the measure by a wide margin if it comes up for a vote. And House Speaker Robert A. DeLeo, a Winthrop Democrat who backs the legislation, says he is confident that a majority in his chamber supports it.
But DeLeo says he is working to secure the two-thirds vote that would be required to override a potential veto from Governor Charlie Baker.
Baker, a Republican, has repeatedly parried questions about where he stands on the matter, saying “the devil is always in the details.” But during his unsuccessful run for governor in 2010, he declared opposition to a similar measure.
The debate has centered on concern about the privacy of women and girls, who might feel uncomfortable with people born with male anatomy who identify as women sharing bathrooms and locker rooms with them.
Seventeen states and more than 200 cities across the country protect transgender people from discrimination in public accommodations, according to Freedom Massachusetts.
Advocates say nearly 200 businesses are backing the legislative effort here, including Harvard Pilgrim Health Care, Google, and Eastern Bank. They are set to announce Monday that Hill Holiday, one of the largest advertising agencies in the country, is joining the coalition. And with the addition of the Patriots, Celtics, Bruins, and Revolution, all of the region’s major professional sports teams will be on the roster.
The Celtics, in a written statement to the Globe over the weekend, said the team is “proud to support efforts that guarantee equal access rights for everyone.”
Advocates say there are no plans, now, for athletes from the teams to advocate for the legislation.
Massachusetts lawmakers approved legal protections for transgender people in housing, employment, lending, and public education in 2011. But they left public accommodations out of the bill amid concerns about bathroom and locker room privacy.
Advocates revived the public accommodations push last year and lobbied intensely for passage of the legislation before the Christmas break before running into resistance in the House.
They say their best chance for passage this year may be in the coming weeks, before the budget process starts to consume the Legislature and the pressures of the coming election make it more difficult to get a vote on an issue that makes some lawmakers skittish.
David Scharfenberg can be reached at email@example.com. Follow him on Twitter @dscharfGlobe.