Montana Rep. Denny Rehberg was no fan of the $58 billion federal rescue of General Motors Co., saying he worried taxpayer money would be wasted and the restructuring process would be vulnerable to "political pressure." Now the lawmaker says it's his "patriotic duty" to wade into GM's affairs.

Along with Montana's two Democratic senators, the Republican congressman is battling to get GM to reinstate a contract with a Montana palladium mine nullified in bankruptcy court. "The simple fact is, when GM took federal dollars, they lost some of their autonomy," Mr. Rehberg says.

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Montana Sen. Jon Tester, at a Stillwater Mine in Nye, Mont., is trying to protect the mine's GM contract.

Federal support for companies such as GM, Chrysler...