The organizers of Boston's St. Patrick's Day Parade have banned a prominent gay veterans group from participating this year.

OutVets made history when the group was allowed to join the parade for the first time in 2015. But, on Tuesday, Boston's Allied War Veteran's Council, which organizes the parade, voted 9-4 not to let them participate in this year's parade on March 19.

"While the reason for our denial is unclear, one can only assume it's because we are LGBTQ," OutVets posted on Facebook. "This is a sad day for the LGBTQ community but also a horrible day for veterans. We served our country with honor and distinction. But even after successfully participating in this parade and bringing honor to those who have served, we are still fighting for the respect that comes with serving our country."

Boston isn't the only city with a checkered history when it comes to LGBT groups and St. Patrick's Day: It wasn't until last year that LGBT groups were invited to participate in New York's St. Patrick's day parade, following decades of protests and boycotts. (Mayor Bill DiBlasio refused an invitation to the parade until the ban was lifted.)

Surprisingly, this sort of discrimination is still legal: the War Veteran's Council took their battle to keep LGBT groups out all the way to the Supreme Court in 1995—and won. The court ruled that private organizations can exclude groups from participating in their public events if they believe their message conflicts with the one organizers are trying to convey.

“I am saddened and outraged that the Allied War Veterans Council has voted to turn back the clock on equality,” Ed Flynn, a City Council candidate and member of the South Boston Allied War Veterans Council, said in a statement.

In the Facebook post, OutVets stipulated that while its followed all the parade rules meticulously, members did complain after being placed at the back of last year's parade, far from other veterans organizations.

"While many wanted to quit and go home, we agreed that as an organization we were there to honor those who had served and are still serving our country," the post stated. "OutVets complained to the organizers about this and thought we had a good working relationship with the council."

The group speculates that the death of their "strongest ally," former South Boston Allied War Veterans Council Commander Brian Mahoney, is the reason that "the old mindset of bigotry and discrimination has crept back into the parade." The council has not responded to requests for comment.

Mayor Marty Walsh says he won't march in the parade if OutVets is excluded: "I will not tolerate discrimination in any form," he said Wednesday morning. "We are one Boston, which means we are a fully inclusive city."

h/t: Boston Globe