(CNN) – While in New York on Tuesday for an event with former New York City mayor Rudy Giuliani, likely GOP presidential nominee Mitt Romney made unannounced visits, including one with the city's mayor, his campaign confirmed to CNN.
Following the meeting, an aide to Michael Bloomberg said the New York City mayor was undecided about making an endorsement in the presidential race, but said "it's possible." Bloomberg won his last election as a political independent, but was previously a Democrat, then a Republican.
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The aide understood it to be Bloomberg and Romney's first meeting.
The two discussed education reform, the economy, and illegal guns, as well as immigration reform, an issue on which Bloomberg has criticized Romney.
As recently as September of last year, Bloomberg criticized Romney's opposition to then GOP-candidate Rick Perry's plan, which included no additional fencing alongside the US-Mexico border, but allowed in-state tuition for the children of illegal immigrants.
"Bottom line is, Romney's wrong on this one," Bloomberg said. "This is the future of America and Perry's right on this one. I don't agree with Perry on other things, but on this one he's right."
Since Friday, Bloomberg has played golf with Vice President Joe Biden and Defense Secretary Leon Panetta. Bloomberg did not make an endorsement in the 2008 race.
While in New York, Romney also attended a memorial service for Mike Wallace, the CBS' "60 Minutes" correspondent, in the city, Romney's campaign said.
On Tuesday afternoon, he is to mark the one-year anniversary of the US attack which killed Osama bin Laden at the event with Giuliani. Giuliani's 2008 presidential bid emphasized his handling of the 9/11 attacks on the city where he was mayor at the time.
– CNN's Mary Snow, Steve Brusk, and Jim Acosta contributed to this report