Republican U.S. Senate hopeful Dan Sullivan has asked Democratic Sen. Mark Begich to sign a pledge aimed at countering third-party spending in the high-profile race.

Sullivan's proposal calls on special interest groups to stop TV and radio ads by July 4 that identify either of them and support or attack their candidacies. If the ads continue, the candidate that benefits from such ads would contribute an amount equal to half the ad buy to a charity the other candidate chooses.

Sullivan didn't mention the other Republicans running. So far, outside groups have focused on him and Begich.