With the aim of depoliticizing a largely Republican assault, the leading lobbying group for small businesses has joined officials from 20 states in their legal challenge to the new health care law. An amended complaint filed Friday in U.S. District Court in Pensacola, Fla., lists the lobbying group, the National Federation of Independent Business, as a plaintiff in the lawsuit that was originally filed in March by attorneys general from 13 states. Attorneys general or governors from another seven states formally joined the lawsuit on Friday. Among the state plaintiffs, only the attorney general of Louisiana, James Caldwell, is not a Republican. Two individuals also joined the litigation. One is the uninsured owner of an automobile repair shop in Panama City, Fla. The other is a man from Washington state who prefers to pay his medical bills out of pocket rather than being compelled to obtain insurance, as will be the case starting in 2014. The additions of the business association and individual plaintiffs, according to lawyers involved, were intended to shift any public perception that the lawsuit was primarily a political device. But the new plaintiffs also may help the states fight an anticipated challenge by the federal government to their standing, or legal authority, to bring the lawsuit. The Florida lawsuit is among at least a dozen filed against the Democratic health care law since President Barack Obama signed it on March 23. Virginia's attorney general has filed a separate case in Richmond, and other lawsuits have been mounted by physicians' groups and conservative legal centers. The cases typically focus on the provision that will require most individuals to obtain commercial or government health insurance, a mandate with few precedents in American policy or jurisprudence. The lawsuits argue that the insurance requirement, by penalizing people for not purchasing a product, represents an unconstitutional extension of Congress' power to regulate interstate commerce. The federal government has responded in court filings that an individual decision to not purchase insurance is, in effect, a decision about how to pay for future medical care. Taken in the aggregate, those decisions substantially affect interstate commerce by shifting the cost of covering the uninsured to policyholders, health care providers and taxpayers, government lawyers maintain. In papers submitted this week in a Michigan case, the Justice Department vigorously attacked the plaintiffs' legal standing to challenge an insurance mandate that does not take effect until 2014, and thus has yet to cause any harm. In the Florida case, the federal government's response -- in the form of a motion to dismiss the lawsuit -- is not due until June 16. Oral arguments are scheduled for September. Although the health care law provides substantial tax credits to small businesses that provide insurance to employees, the National Federation of Independent Business wound up opposing the legislation because of what it viewed as unacceptable mandates and costs for its members. 'The outpouring of opposition to this new law was overwhelming,' said Dan Danner, the group's president, 'and our members urged us to do everything in our power to stop this unconstitutional law.' 