Michael R. Bloomberg, the billionaire mayor of New York, is throwing a fund-raiser for Senator Scott Brown, bolstering Brown’s credentials as a business-friendly independent.

Bloomberg’s support could help Brown, a Massachusetts Republican locked in a reelection fight against Democrat Elizabeth Warren, shield himself from critics who say he marches in lockstep with Washington Republicans.

Bloomberg, a Massachusetts native, was born in Allston and grew up in Medford.

Advertisement - Continue Reading Below

“Mayor Bloomberg is a true independent who always puts progress over politics,” Brown’s spokesman, Colin Reed, said in a statement today. “That’s Scott Brown’s philosophy as well, and he is honored to have the mayor’s support.”

According to a copy of the invitation for the event, first reported by Politico, the fund-raiser will take place Aug. 15 at the mayor’s Upper East Side townhouse. Donors are asked to give between $1,000 and $5,000 to Brown’s reelection campaign.

A Bloomberg spokesman, Stu Loeser, said the “biggest reason” the mayor decided to support Brown was Brown’s opposition to an NRA-backed bill, known as the National Right-To-Carry Reciprocity Act, that would allow gun owners to carry concealed weapons across state lines.

Bloomberg, who is co-chair with Boston Mayor Thomas M. Menino of a group called Mayors Against Illegal Guns, has made gun control one of his top issues.

In November, Brown, who drew financial support from the National Rifle Association in his 2010 run for Senate, announced he would oppose the bill.

“In Albany and Washington, when legislators take a tough vote for the people of New York against their party’s or special interests’ orthodoxies, the mayor appreciates it and is inclined to show his support,” Loeser said.

Bloomberg, an independent, has made a career of shunning party orthodoxy.

He has infuriated Republicans by banning the sale of large sodas, pushing for stricter gun laws, and seeking to impose congestion pricing on motor vehicle traffic into the city. At the same time, the mayor has angered Democrats by defending Wall Street and refusing to endorse President Obama.

Both Obama and Mitt Romney have courted the mayor’s endorsement this year.

Warren, meanwhile, announced Thursday afternoon that she will receive an endorsement in Worcester from the Credit Union League, which represents 200 credit unions.

She is hoping to use the endorsement to underscore her message that she is a consumer advocate in favor of small banks that avoid exotic investments.