BILLINGS, Mont. (AP) — Democratic lawmakers called for an investigation Thursday into U.S. Interior Secretary Ryan Zinke’s involvement in a land deal with the chairman of an energy services company that does business with his agency.

A foundation created by Zinke and run by his wife, Lola, has been dealing with a company co-owned by Halliburton Chairman David Lesar on a commercial development in Whitefish — Zinke’s hometown.

The foundation is allowing Lesar and his family to use a portion of its land as a parking lot for the development. The land was donated to Zinke’s Great Northern Veterans Peace Park Foundation 10 years ago to create a park, but remains largely untouched.

Democrats led by Rep. Raul Grijalva of Arizona on Thursday asked Interior Department Inspector General Mary Kendall to examine whether Zinke was using his office for personal financial gain.

The lawmakers released emails obtained under a public records request showing Zinke met with Lesar, his son John Lesar and Montana developer Casey Malmquist at the secretary’s office last August.

The meeting took place more than five months after Zinke left the foundation involved in the real estate deal. Under Zinke’s watch, the Interior Department has pushed to increase drilling on public lands and eased restrictions on the oil and gas industry — moves that could directly benefit Halliburton.

“The email and meeting with Malmquist and the Lesars raises troubling questions,” the lawmakers wrote in a letter to Kendall. “The American people must be able to trust that Department of the Interior decisions that affect the nation’s welfare on a daily basis are not compromised by individual self-enrichment.”

In addition to Grijalva, the letter was signed by Rep. Donald McEachin of Virginia and Rep. Jared Huffman of California.

Zinke spokeswoman Heather Swift did not immediately respond to a request for comment. She previously said the land deal was “not a departmental matter.”

A Halliburton spokeswoman, Emily Mir, has said that the real estate deal was Lesar’s personal investment and had nothing to do with the company. She said Thursday that the company had “nothing further to say.”

Malmquist could not be immediately reached for comment.

The land in question was donated by BNSF Railway in 2008 to Zinke’s Great Northern Veterans Peace Park Foundation to create a park for children to sled and skate in the winter. Immediately adjacent to the park is an abandoned mill where Lesar plans a hotel, microbrewery, art gallery and office space.

The Whitefish City Council approved a zoning change for Lesar’s project in January, with one of the conditions that the developers sign an agreement with the foundation to build a parking lot that will benefit both the park and the commercial development.

The agreement gives Lesar foundation land for a parking lot and a separate easement to access the property.

Whitefish city planner Dave Taylor said earlier this week that Lesar’s plans pre-dated Zinke becoming Interior Secretary early last year. The project wouldn’t be able to proceed without the developers coming to an agreement with Zinke’s foundation, Taylor said.

The Western Values Project, a Whitefish-based group run by former Democratic operatives that’s been an outspoken critic of Zinke, said Thursday it had obtained calendar entries for Zinke that show he met with industry representatives including from Halliburton in April, 2017. It’s not known what was discussed.