Backers of initiatives to expand voting urged a federal judge on Thursday to block a new law that imposes a $3,000 limit on contributions to political committees collecting petition signatures to put proposed constitutional amendments on the ballot.

The American Civil Liberties Union of Florida and three political committees are challenging the law, arguing the contribution limit imposes an unconstitutional burden on political speech. Republican lawmakers passed the cap in April as part of a years-long effort to make it more difficult for citizens to amend the state Constitution.