DENVER (AP) _ Opponents of a gun-control ballot initiative backed by President Clinton challenged the proposal in the Colorado Supreme Court on Monday, forcing sponsors to hold off gathering signatures for now.

The initiative, scheduled to be on the November ballot, would require background checks on all gun sales at gun shows.

William Herpin Jr. of Colorado Springs challenged the measure, saying it violates the state Constitution because it covers more than one subject.

The state Title Board has already rejected that challenge and approved the initiative for the ballot.

Sane Alternatives to the Firearms Epidemic, sponsor of the initiative, has until August to gather more than 62,000 signatures of Colorado voters.

Herpin's challenge will force SAFE to wait weeks before collecting signatures. SAFE co-founder Arnie Grossman has called the legal challenge a delay tactic.

Clinton visited Colorado two weeks ago at SAFE's invitation to endorse the initiative, which SAFE decided to take to the ballot after the Legislature killed a similar measure.

SAFE was formed after the 1999 shootings at Columbine High School, in which the two teen-age gunmen used weapons bought through private dealers at a gun show.