Boston Mayor Marty Walsh is not participating in South Boston's St. Patrick's Day parade.

Organizers behind Sunday's parade – the nation's second largest behind New York – continue to exclude gay groups from marching.

“So much of our Irish history has been shaped by the fight against oppression,” Walsh, the city's first Irish-American mayor in 20 years, said in a statement.

A deal brokered by Walsh which would have allowed MassEquality, the state's largest LGBT rights advocate, to march in the parade fell apart last week.

“As mayor of the city of Boston, I have to do my best to ensure that all Bostonians are free to participate in the civic life of our city. Unfortunately, this year, the parties were not able to come to an understanding that would have made that possible.”

Walsh's decision comes after Sam Adams pulled its sponsorship of the parade.

(Related: Heineken pulls support from St. Pat's Day parade over gay exclusion.)