A super PAC founded and funded by billionaire Charles Koch reported $34,000 in spending to support Rep. Henry Cuellars (D-Texas) primary campaign, according to a Friday filing with the Federal Election Commission.

This is the first time that Americans for Prosperity Action is backing the election campaign of a congressional Democrat.

Cuellar, a seven-term incumbent, is facing a tough primary challenge from immigration and human rights lawyer Jessica Cisneros. He has one of the most conservative voting records among Democrats in Congress despite representing a safe Democratic seat. His reelection is supported by large national and Texas corporations and business associations, including the American Bankers Association, Texas Bankers Association, the U.S. Chamber of Commerce and the Laredo Chamber of Commerce.

Cisneros has won endorsements from Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.) and Rep. Alexandria Ocasio-Cortez , national and local progressive groups, including Justice Democrats, womens groups, environmental groups, as well as labor unions like the Service Employees International Union and the local Texas AFL-CIO.

Koch Industries, Inc., the giant oil and gas services corporation owned by Charles Koch, is the largest donor to Americans for Prosperity Action this election cycle, giving $3 million. The group is the super PAC arm of the larger nonprofit Americans for Prosperity. The nonprofit group was founded by Koch and his late brother David Koch to advance a free market and libertarian policy agenda in the United States. It played a pivotal role in funding the anti-Obama administration Tea Party in 2010.