NEW YORK — Eliot Spitzer is facing a challenge to his bid to get on the ballot in the city comptroller's race, after a Republican strategist contested the ex-governor's petition signatures.

E. O'Brien Murray filed an objection shortly before a midnight deadline Monday. He said he reviewed the more than 27,000 signatures that Spitzer, a Democrat, gathered in a four-day burst and found errors. Murray has a week to file details of his claims.

Spitzer's campaign said Tuesday it's not worried about its petitions, which count more than seven times as many signatures as needed.

"The Spitzer campaign took great care in the petitioning process," Martin O'Connor, a lawyer for the campaign, said in a statement.

Five years after resigning amid a prostitution scandal, Spitzer embarked on his surprise campaign to return to politics July 8, four days before the deadline to submit signatures. His self-financed campaign paid canvassers to gather them.

Several of Spitzer's rivals had said they wouldn't challenge his signatures; his Democratic primary opponent, Manhattan Borough President Scott Stringer, also asked his supporters not to do so. But Murray said he felt Spitzer shouldn't be able to march onto the ballot without a fight.

"Eliot Spitzer doesn't deserve a free pass after what he put New York through," Murray told the New York Post, which first reported the story Monday night. He didn't immediately respond to a message Tuesday .

Murray, known as "O'B.," managed Republican Bob Turner's successful campaign for Congress in a 2011 special election and conservative Democrat Simcha Felder's successful state Senate run last year.

Petition signature problems can include missing dates, unclear addresses, voters or canvassers who aren't registered in the candidate's party, or voters who already signed a petition for another candidate in the same race.

If Murray files detailed objections by next week's deadline, city Board of Elections staffers will review them and examine Spitzer's petition signatures, and the board will hold a hearing, starting July 30, to decide whether to invalidate any signatures.