New York City Mayor Michael Bloomberg plans to unveil a campaign to sell the most populous U.S. city as a gay-wedding destination after thousands marched to celebrate the state’s legalization of such marriages.

The “NYC I Do” campaign “will create millions of dollars in additional economic impact to the city’s $31 billion tourism industry,” Kimberly Spell, a spokeswoman for New York & Company, the city’s marketing office, said yesterday in an e- mail. Bloomberg will unveil more details in coming days, she said.

Governor Andrew Cuomo signed a law June 24 to grant marriage licenses to same-sex couples after the Republican- controlled state Senate approved it. Passage came about a month after a group of Democratic state senators issued a report finding New York stood to reap $391 million from areas including economic activity and tax revenue within three years.

The benefit to Massachusetts’ economy was worth more than $100 million over five years after legalizing same-sex marriage, according to the institute.