U.S. Senator Ron Johnson filed a lawsuit on Monday challenging the way President Barack Obama's healthcare law is being applied to Congress, part of a larger Republican strategy to draw attention to what they see as critical flaws in Obama's signature domestic policy.

Johnson, of Wisconsin, is challenging a U.S. agency decision allowing the federal government to keep paying part of the costs of health insurance for U.S. lawmakers and their staffs who must buy coverage through the Obamacare marketplaces.