New York City Mayor Michael Bloomberg says he'll spend $500,000 of his personal fortune on gay marriage campaigns in Maine, Minnesota and Washington state to help them raise an equal amount.

Monday's announcement follows up on a political spending push the billionaire businessman-turned-politician announced last week. He said then that he planned to spend at least $10 million before Election Day promoting moderate candidates and ballot measures supporting gay marriage.

Bloomberg has pledged a total of $325,000 to groups backing ballot initiatives that would legalize gay marriage in Maine and uphold it in Washington.

He's giving another $125,000 to a group working against a Minnesota constitutional amendment that would strengthen an existing law against same-sex marriage.

Bloomberg announced a $250,000 contribution to a Maryland gay marriage initiative earlier this month.