A Colorado group is airing radio advertisements in Casper and Cheyenne against a proposed immigration overhaul bill before the U.S. Senate.

The ad by the Rocky Mountain Foundation in Littleton, Colo., does not mention Wyoming Sens. Mike Enzi or John Barrasso by name.
    
But foundation chairman Tom Tancredo tells the Casper Star-Tribune that their votes are important because he believes the proposal will pass or fail on one or two votes.
    
Tancredo opposes the proposal's pathway to citizenship for the estimated 11 million immigrants living in this country illegally.
    
Enzi and Barrasso have not indicated how they will vote on the proposal, which is expected to come before the full Senate this month.
    
The Republican-led House is working on its own immigration bill.