New York City Mayor Mike Bloomberg plans to host a fundraising event in August for Republican Sen. Scott Brown (MA), who is being challenged by Harvard law professor Elizabeth Warren.

“The biggest reason the mayor is supporting Senator Brown is the senator’s help on one of our biggest gun issues: opposing concealed-carry reciprocity that would let people with gun permits from rural states like Arkansas and Kentucky carry hidden handguns in New York City,” Bloomberg spokesman Stu Loeser told the New York Times.

Bloomberg, who co-founded Mayors Against Illegal Guns, has called on President Barack Obama and Republican presidential candidate Mitt Romney to provide substantive solutions to the problem of gun violence in the wake of the Colorado theater mass shooting.

But Capital New York notes that Brown had an 'A' rating from the National Rifle Association in 2010. While Brown supported a state assault weapons ban, he opposed similar legislation at the federal level. Warren, his opponent, supports a federal ban on assault weapons.

Politico suggested Bloomberg favored Brown over Warren because of his ties to Wall Street. Bloomberg, a billionaire, has been a champion of the financial sector, while Warren has been critical of Wall Street, calling for extensive reforms.