The union, which plans a formal announcement Tuesday in front of a shuttered fire station, has had a ragged relationship with Nutter for much of the last four years, often accusing him of endangering the public with budget cuts to the Philadelphia Fire Department.
"I don't know that I had to do a lot to sway them," Street said of the endorsement. "I'm pro-safety. I'll always be pro-safety."
Street said he is now crunching numbers to see if he can restore some of Nutter's budget cuts that upset the union. He declined to comment further until Tuesday.
"I don't want to make statements and commitments I can't keep," he said. "I'm putting that together right now."
Bob Bedard, a union spokesman, said the endorsement was meant to "send a signal" and draw attention back to the concerns of firefighters in the city.
Bishop Leonard C. Goins, founder of the Pentecostal ministers group, said he was moved to support Street based on a letter to the editor he wrote to the Daily News. Street, who compared himself to Moses in that letter, served 26 months in federal custody for not paying taxes on $3 million in income from 2002 to 2004.
"We believe in God and a second chance," Goins said. "I think he is genuine in saying he deserves a second chance. He made a mistake. He paid for it."
Goins supported Republican Sam Katz in his 2003 bid to unseat then-Mayor John Street, Milton's younger brother.
Goins is also critical of Nutter's stop-and-frisk approach to combating violent crime, saying it unfairly targets African-American men. His group, which represents nearly 100 churches, endorsed Republican Tom Corbett for governor last year and Democratic U.S. Rep. Joe Sestak for the U.S. Senate. Goins delivered the benediction in January at Corbett's inauguration.
Nutter on Monday received the endorsement of the Philadelphia Council of Clergy, which says it has about 150 active members.