It would be more difficult for Marylanders to challenge laws through voter referendums under a constitutional amendment being considered by the Maryland Senate.

Maryland is one of 27 states that allow voters to overturn laws by gathering signatures to put them on a ballot in a process known as a referendum. The bill, sponsored by Sen. Richard Madaleno Jr., D-Montgomery County, would require petitioners to gather more signatures to put a law up for referendum.

Madaleno did not respond to a call for comment, but legislative leaders have said the referendum process has to be looked at because it might be too easy to put laws on the ballot. That came after voters petitioned three laws to referendum in 2012, after 20 years with none.

Maryland good-government groups aren't happy with the proposed requirements.

"We are concerned that Madaleno's bill would raise the bar, making it that much harder for citizens to have their voices heard," said Jennifer Bevan-Dangel, executive director of Common Cause Maryland.

"The petition process, in the states that have both initiative and referendum, has seen reforms to how redistricting occurs, reforms dealing with campaign finance law and ethics laws. Sometimes people have a clearer view of things than the legislature."

Maryland's constitution allows voters to put to referendum all new bills, except budget bills and measures involving the manufacture and sale of liquor. Petitioners are required to gather signatures equal to 3 percent of the number of people who voted in the most recent governor's race. Given that about 1.9 million people voted in the 2010 contest, that means petitioners would have to gather about 55,000 signatures to put a law on the ballot.

Madaleno's amendment would change that to 5 percent of the total number of registered voters. With about 3.8 million registered voters in Maryland, petitioners would need about 188,000 signatures under the new rules -- more than three times as many.

Sara Love, public policy director for the Maryland chapter of the American Civil Liberties Union, said the ACLU doesn't oppose the 5 percent requirement -- she noted most states with referendums require between 5 and 12 percent of the number of votes cast in the last governor's race -- but the ACLU is opposed to requiring that percentage to come from the number of registered voters.

"We object to that because we believe that is placing a larger hurdle to the referendum right Maryland citizens have," Love said. "Under our constitution, Maryland citizens have been given the right to petition laws they do not agree with to referendum, and we have incorporated that into our democratic fabric."