A federal judge has set a June 20 hearing date for a lawsuit filed by the state of Oklahoma challenging an IRS ruling related to President Obama’s health care law.

As I described the suit in March:

Under the law, if states choose not to set up their own insurance exchanges, then the federal government steps in to set up a federal exchange. But here’s the catch — the text of Obamacare stipulates that the subsidies (valued at about $1 trillion over a decade) apply to state-based exchanges, but not to exchanges run by the federal government.

With 26 states having made the decision to default to a federal insurance exchange — set to be fully operational by next January — this is now a very pressing legal question. The Internal Revenue Service has ruled, despite the text of the law, that the subsidies should apply regardless of whether the exchange is a state or federal one. But Oklahoma challenged that ruling last September in the Eastern District of Oklahoma.

“We are very bullish on the merits of that case,” Oklahoma Attorney General Scott Pruitt said during a visit with The Washington Examiner. “We’ve had private plaintiffs join us. It’s been fully briefed. … It’s all about black-letter law. It’s all about the IRS not respecting what Congress said and doing something inconsistent with what the statute said.”

The June 20 hearing will revolve around attempts by the federal government to have the suit thrown out.