Former Wisconsin U.S. Sen. Russ Feingold says plans by Wisconsin-based Johnson Controls to move its headquarters to Ireland to cut the company's tax bill are a sign that the rules needs to be tightened.

As part of its merger with Tyco International, Johnson Controls will shift its global headquarters from the Milwaukee suburb of Glendale to Cork, Ireland. The company is expected save $150 million a year on federal corporate taxes.

Democrat Feingold, who's running to reclaim his U.S. Senate seat, told a Marquette University forum that Johnson Controls is a great company, but Congress should get behind a measure authored by Illinois Sen. Richard Durbin.

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"And what Sen. Durbin's bill does is say, 'Look, if you're not really moving your business over there, if it's not really a foreign operation, under that scenario, you don't get the same benefit,'" Feingold said.

Incumbent Republican U.S. Sen. Ron Johnson has instead advocated for doing away with U.S. corporate taxes or lowering them dramatically.

Feingold said he might consider supporting a small reduction in the corporate tax rate if firms bring money back to the U.S.