New York City Mayor Michael Bloomberg will co-host a fundraiser for the four GOP senators who voted in favor of a gay marriage bill, the Times-Union reported.

Next month's Manhattan fundraiser will benefit Republican Senators Stephen Saland of Poughkeepsie, James Alesi of Rochester, Roy McDonald of Saratoga and Mark Grisanti of Buffalo.

Tickets run as high as $16,800, the election law's current maximum donation to a campaign. ($10,300 for the campaign, plus a $6,500 contribution for potential primary challenges.) Bloomberg has already donated the maximum allowed to the four senators.

The event is co-chaired by Bloomberg, gay philanthropist Tim Gill and Elliot Management Corp. CEO Paul E. Singer. Singer has been described by The New York Times as “one of the most generous Republican donors in the country.” The invitation also lists representatives from Marriage Equality New York (MENY), the Gill Action Fund and the Human Rights Campaign (HRC), the nation's largest gay rights group.

The National Organization for Marriage (NOM), the nation's most vociferous opponent of marriage equality, has vowed to work to unseat the four GOP senators. The group's campaign so far has included erecting billboards and mailing out fliers. A billboard located in McDonald's district reads: “Roy McDonald, You're Fired!” NOM's plan to repeal the marriage law hinges on growing a majority in the Legislature to approve a constitutional amendment for the 2015 ballot.