A group representing small businesses is asking the U.S. Supreme Court to strike down the Obama administration’s overhaul of the health care system.

The National Federation of Independent Business filed an appeal with the nation’s top court Wednesday, asking justices to declare the entire law unconstitutional. They are appealing a court decision made last month that upheld most of the law except a provision requiring all Americans to pay for health insurance or face a penalty.

The group argues in court papers that the so-called “individual mandate” is central to the health care law, and if it is unconstitutional, the entire law must be invalidated.

The filing asks the Supreme Court to rule during its upcoming session, which runs until June 2012. The business group says it is important for entrepreneurs to know if they will have to pay costs related to the new health insurance standards.

The group had been joined in its legal challenge by 26 states. The states have not filed an appeal with the Supreme Court.

Obama administration officials have defended the need to require all Americans to have health insurance.

In the August decision, a federal appeals panel wrote that the individual mandate goes too far, representing a “potentially unbound assertion of congressional authority.”

Other court rulings have upheld the law, including the individual health care insurance requirement.