By John S. McClenahen Three powerful business-lobbying groups in Washington, D.C. -- the United States Chamber of Commerce, the National Association of Manufacturers and the National Association of Wholesaler-Distributors -- are formally challenging U.S. campaign finance reforms enacted last month. The trio filed suit on April 22 claiming the law places unconstitutional restrictions on free speech. Specifically being challenged are provisions of the law that limit so-called issue advocacy campaigns and impose a ban on the broadcast of issue ads 30 days before a primary election and 60 days before a general election. The law is to take effect on Nov. 6, one day after this fall's Congressional elections. The suit is expected to be heard initially by a by a three-judge panel in the District of Columbia.