INDIANA — The state of Indiana and 15 of its public school districts sued the U.S. government this week, challenging its use of federal tax subsidies and penalties to implement President Barack Obama’s 2010 healthcare law.

The lawsuit claims that a rule, issued in 2012 by the Internal Revenue Service which allows the federal government to provide tax subsidies for individuals to buy health insurance on federal exchanges, contradicts what Congress originally intended in the Affordable Care Act.

The healthcare law had stated that individuals who obtain health insurance through an exchange “established by a state” qualify for a federal tax subsidy. Later on however, the IRS added in its rule that the tax subsidies would be available to people who bought insurance on both state and federal exchanges.

In their lawsuit, Indiana and its school districts argue that the purpose of that provision was to force states to set up their own exchanges.

The lawsuit is one of at least three challenging the IRS rule, including one filed by Oklahoma’s Republican Attorney General Scott Pruitt and another brought by a group of private employers in Washington, D.C.

The Indiana lawsuit claims that applying the subsidies and penalties in the state violates the Affordable Care Act and infringes on Indiana’s right to state sovereignty under the U.S. Constitution’s Tenth Amendment.