The Maryland Senate is expected to begin debate on the marriage equality bill Thursday as opponents plan amendments intended to derail the proposal that narrowly passed the House of Delegates last week.

The Associated Press reports that Senate President Thomas V. Mike Miller, who postponed the debate from Wednesday upon request of Republican leaders, said that discussion could continue into Friday before a final vote is taken. A Senate panel advanced the measure in a 7-4 party line vote on Tuesday.

The bill passed the House last Friday in a 72-67 vote, including amendments that would delay its effective date from October 2012 to January 2013 and keep the law from taking effect until any litigation related to a potential referendum is processed. According to the AP, opponents of the bill asked Attorney General Doug Gansler for feedback on the constitutionality of the amendments, and his office sent letters that confirmed their soundness. Any changes in the Senate version would force the bill back to the House, where approval for a second time would not be guaranteed.

Reuters reports that opponents in the Senate are considering amendments that would change the effective date of the law back to October 2012 and broaden its religious liberty protections. Still, Senate leaders expect to pass the bill, which passed for the first time last year in a 25-21 bipartisan vote.

Governor Martin O’Malley has vowed to sign the bill, but opponents plan to push for a referendum. According to Reuters, some 56,000 signatures would be needed to put the measure on the ballot this November, one-third of which would have to be submitted by May 31 and the remainder by June 30.

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