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The U.S. Chamber of Commerce is planning a broad effort to blunt the health overhaul by trying to shape its regulatory language and spending heavily to unseat vulnerable Democrats who voted for it.

The campaign is the latest example of the escalating tensions between proponents of the health overhaul and big businesses, which have become more specific in their criticisms of the new law.

In recent days, a handful of large companies have reported hefty charges because the law eliminates a tax deduction for firms that offer prescription-drug coverage to retirees.

In a letter to board members Monday, chamber president and chief executive Thomas J. Donohue said the business lobby will seek changes to regulations to "minimize the potentially harmful impacts of this bill on our members and the country." If regulators "exceed legislative mandates or try for end-runs around the lawful rule-making process," he wrote, the chamber "will take legal action."

Mr. Donohue also said the group planned to spend $50 million this summer and fall to ensure that voters in pivotal House and Senate races know where lawmakers stand on health and other big issues. The chamber spent $36.4 million in the 2008 election.

At the heart of the effort will be a team of chamber staff that will "participate in the years-long process of writing the thousands of pages of federal regulations that will implement the many provisions of this legislation," Mr. Donohue wrote.

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