Updated

Missouri Senate Democrats are waging a filibuster Tuesday to block a vote on a proposed amendment to the state constitution that would grant greater protections to individuals, religious organizations and some businesses opposed to gay marriage.

The measure would ban government penalties against individuals and businesses that refuse on religious grounds to provide goods or services of "expressional or artistic creation" for marriage ceremonies or celebrations of same-sex couples. That could include protections for florists or bakers, who in other states have faced legal challenges for declining to provide services for same-sex weddings.

Clergy and religious leaders also wouldn't face government punishment for refusing to marry same-sex couples, and places of worship that close their doors for those weddings would be protected.

Debate on the bill began around 4:20 p.m. Monday and stretched without a break into Tuesday morning as Democrats stalled a vote. Some opponents vowed to carry on past the 24-hour mark. Republican supporters also pledged to press forward for as long as it takes.

"We're committed to getting it done," said sponsoring Sen. Bob Onder, a Republican from Lake St. Louis.

Onder said the goal of the measure is to prevent the government "from persecuting folks who live out their religious beliefs." He said it is intentionally crafted to be narrower than other recent measures that have faced a backlash — for example, a proposal in Indiana that was criticized by businesses.

Republican lawmakers in various states, including Georgia and West Virginia, have pushed similar measures following the U.S. Supreme Court decision last June that legalized gay marriage nationwide. A constitutional amendment also has been proposed in Oklahoma, and Florida lawmakers last week sent Republican Gov. Rick Scott a bill to specify that churches can't be forced to marry same-sex couples.

If passed by the Senate, the Missouri measure also would have to go through the House before being submitted to statewide voters in either the August primary or November general election.

House Speaker Todd Richardson said Tuesday that lawmakers feel an urgency to act this election year; otherwise, the amendment might have to wait until the 2018 ballot.

"Religious liberty is important, and we've got a lot of people who are talking about it," said Richardson, a Republican from Poplar Bluff.

The Democratic filibuster in the Senate is one of the few tactics the minority party can use to fight bills with strong Republican backing.

Democrats argued the measure unfairly targets same-sex couples and could mean the state loses out on prospective employees turned off by the policy.

Democratic Sen. Jill Schupp, of the St. Louis suburb of Creve Coeur, said some individuals, businesses and organizations "would be given permission to discriminate" if the amendment is approved.

The Supreme Court's ruling effectively invalidated a Missouri constitutional amendment limiting marriage to one man and one woman. That amendment had been approved by 70 percent of Missouri voters in 2004 — making Missouri the first state to add a gay-marriage ban to its constitution after the Massachusetts Supreme Court permitted gay marriage in that state.

Missouri also is one of more than 20 states with religious objection laws already in place. Missouri law bans state and local government agencies from substantially limiting a person's right to follow their religious beliefs unless there is a compelling reason to do so.

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Associated Press writer David A. Lieb contributed to this report.