A conservative group will try to collect enough signatures to force a referendum on a law approved by the General Assembly this year protecting the rights of transgender individuals.

MDPetitions.com, founded and led by Republican Del. Neil Parrott of Washington County, announced Tuesday that it is launching an effort to put the law on the November ballot. If the group collects enough signatures, voters would decide whether to uphold or overrule the law.

The legislation passed both the Senate and House of Delegates by wide margins over the opposition of most Republicans and some socially conservative Democrats, and Gov. Martin O'Malley has said he will sign it. It is scheduled to take effect Oct. 1, but if it goes to referendum, the law would be delayed pending the outcome.

Supporters of the referendum drive would have to collect about 18,500 signatures by May 31 to keep their effort going, Parrott said. If they can meet that goal, they would have to reach a total of 55,736 validated signatures by June 30.

Parrott said MDPetitions.com's initial goal is to collect 25,000 signatures in May and 75,000 by the end of June.

Del. Kathy Szeliga, a Harford County Republican, said the voters she talks to as she goes door to door in her re-election campaign oppose the law.

"People who know about this bill that I'm talking to are shocked and upset about it," she said.

But supporters are confident that he referendum effort will fail.

"Delegate Parrott is going to have an uphill battle to convince Marylanders to repeal fairness for all Marylanders," said Keith Thirion, director of advocacy for Equality Maryland, which worked for passage of the law.

Among other things, the legislation protects transgender people against discrimination in employment and housing. It also upholds a transgender person's right to use public bathrooms and locker rooms for the gender with which they identify.

Those provisions have prompted opponents to label the measure "the Bathroom Bill" and to warn that it would make it easier for sexual predators to gain access to women's bathrooms and locker rooms.

Thirion said the law would apply only to people who have shown that they clearly identify with one gender, and not to a man who might put on a dress to sneak into a women's bathroom. Supporters note that any illegal acts committed by a person in a bathroom remain illegal.

MDPetitions.com has had a strong track record in putting measures on the ballot using its Web-enabled signature-gathering capability. It has not had success in winning those battles at the polls. In 2012, for instance, the group helped force votes on questions about same-sex-marriage, in-state tuition for students who are in the country illegally and on congressional redistricting. Voters upheld all three laws.

michael.dresser@baltsun.com