Two Montana groups are trying to do what has only been done once in 18 years: block a bill by petition.

One proposes to prevent sweeping changes to the state's medical marijuana law. The other wants to block a law that gives utilities the power of eminent domain.

If they get signatures from 5 percent of the registered voters in 34 districts, a referendum will be held in the 2012 general election.

If they get the signatures of 15 percent from 51 districts, they can suspend the bill from becoming law until that election.

Legislative referenda are rare in Montana. They've only been tried three times since 1993. Only once was one successful in suspending a bill.

John Vincent, an organizer of the eminent domain petition, says that's no deterrent.

Story from The Associated Press