Two House Republican chairmen subpoenaed Treasury Secretary Jack Lew on Wednesday for all documents explaining how the government is funding an optional health program created by Obamacare.

Energy and Commerce Chairman Fred Upton, R-Mich., and Ways and Means Committee Chairman Kevin Brady, R-Texas, were threatening a subpoena last week, and made good on their threat Wednesday evening.

The two chairmen have been demanding an explanation of how the Department of Health and Human Services has been funding the Basic Health Program, which states can use to cover low-income people by purchasing plans outside the Obamacare marketplaces. While the program was created by Obamacare, Congress never funded it, but the Obama administration has somehow been diverting billions to the program.

"What's the self-proclaimed 'most transparent administration in history' trying to hide?" the two lawmakers asked. "Subpoenas should not be necessary to gather basic information about $5 billion in unlawful payments to insurance companies, but the Obama administration has left no choice despite our repeated, good faith efforts."

"After almost a year of repeated excuses and stonewalling, the public deserves better. At the end of the day, the American public will get answers," they said.

The lawmakers said they've been asking for information for almost a year now, but with no results to show for it.

In addition to Lew, the lawmakers subpoenaed the chief counsel, the chief financial officer and the deputy chief financial officer for information.