(CNN) A group representing gay veterans says it was denied entry to Boston's St. Patrick's Day parade over a rainbow flag, reigniting a tense issue that had seemingly been resolved and sparking promises of a boycott from the mayor and other elected officials.

OutVets, a group that represents US veterans who identify as LGBTQ, participated in the past two South Boston parades.

The group said it was rejected from this year's version by the local Allied War Veterans Council, which organizes the parade.

The council on Thursday said OutVets has not been officially told it cannot march.

In a statement, the council said OutVets was "informed that our Code of Conduct prohibits 'the advertisement or display of one's sexual orientation,' and that the 'rainbow' flag on its banners and logo was in violation of this rule."


'Heated' meeting over reason

OutVets, parade organizers and the Allied War Veterans Council of South Boston met Wednesday afternoon in an attempt to solve the issue, OutVets founder Bryan Bishop said.

The meeting became "heated," Bishop said, after the council said OutVets was denied entry because the banner includes a rainbow flag.

Bishop declined to change the rainbow in the logo, and said it's the same design used when veterans marched for the past two years. "What about this depiction of color represents sexuality? I don't understand that. It's just crazy, it really is," Bishop said Wednesday. "People are outraged, people are very upset."

Bishop said he was heartened by the support OutVets has received from the public and elected officials, "but it doesn't take away the fact of how angry we are that this happened again."

"This is not a political issue," Bishop said. "This is an issue of discrimination against those who served."

The Allied War Veterans Council said it has received hate-filled emails from people "who are uniformed of the facts." It said OutVets also did not submit its application before the deadline and that the parade is not intended as a political advocacy platform.

The matter may be considered again Friday. "We hope for a positive resolution to this situation," OutVets said on Facebook.


'Outrageous and disgraceful'

OutVets, in a Facebook post, said, "We served our country with honor and distinction. But even after bringing honor to this parade, this community, and to all those who have served, we fight every day to be treated with the basic dignity that comes with service to country."

The Allied War Veterans Council of South Boston had for years banned gay groups from participating in the parade, before finally allowing them to participate in 2015. The council reportedly voted 9-4 to keep the group out of the March 19 parade.

The decision prompted a backlash and promises of a boycott from a number of prominent local officials. Mayor Martin Walsh said he will not march in the parade unless the issue is resolved, and encouraged others to boycott it as well.

"I will not tolerate discrimination in our city of any form. We are one Boston, which means we are a fully inclusive city," Walsh said on Facebook.

Massachusetts Gov. Charlie Baker, a Republican, said he would probably not attend if OutVets was not allowed to march.

"The idea that we would restrict the opportunity for men and women who put on that uniform, knowing full well they could put themselves in harm's way, and deny them an opportunity to march in a parade that's about celebrating veterans doesn't make any sense to me," Baker said, according to WCVB.

"If veteran's groups aren't allowed to march in that parade for whatever reason, then I'll probably do something else," Baker said.

US Rep. Seth Moulton, a Marine veteran who has previously marched with OutVets, said the decision was "outrageous and disgraceful" and said he, too, would boycott.

Dan Magoon, executive director of Massachusetts Fallen Heroes and a veteran himself, said he resigned as chief marshal of the parade.

"The fact that this group wasn't allowed in the parade, I didn't see fit to march without them," Magoon said. "I decided if they were not gonna be a part of it, neither was I."


An old issue returns to the fore

LGBTQ groups have a lengthy and tense history with the South Boston St. Patrick's Day parade.

In 1992, the Irish-American Gay, Lesbian and Bisexual Group of Boston, or GLIB, requested to march in the storied parade, but the South Boston Allied War Veterans Council denied their application.

GLIB sued, claiming that the decision was a form of illegal discrimination. The case eventually reached the US Supreme Court, which ruled against GLIB in 1995.

Still, the controversy led the city to pull public funds from the parade, and longtime Mayor Tom Menino boycotted the parade for two decades.

It took until 2015 for the council to allow an LGBT group to participate. That year, OutVets marched for the first time, and Walsh became the first active Boston mayor to participate in the parade in years.