The chairman of the House Committee on Homeland Security on Wednesday called for an investigation into a $400 million border wall contract awarded this week to North Dakota-based Fisher Sand and Gravel, a company President Trump personally urged military officials to hire.

In a letter to the Defense Department Office of Inspector General, Rep. BennieThompson (D-Miss.) said there are reasons to be suspicious of the decision to bestow such a large contract on the company. Thompson cited Trump’s repeated promotion of Fisher to the U.S. Army Corps of Engineers and a recent visit by the acting secretary of the Department of Homeland Security to a span of privately financed barrier the firm built outside El Paso.

“These actions raise concerns about the possibility of inappropriate influence on USACE’s contracting decision,” Thompson wrote. “Therefore, I am requesting that you review the award of this contract to ensure that the bid submitted by Fisher Sand and Gravel Co. met the solicitation standards and that USACE made the award in accordance with federal procurement law and regulations.”

On Monday, the Defense Department said the Army Corps had selected Fisher to build 31 linear miles of new border barrier across the southern edge of the Cabeza Prieta National Wildlife Refuge near Yuma, Ariz.

Fisher’s price tag — approximately $13 million per mile — was lower than the two other companies that bid on the contract, according to one administration official with knowledge of the contract.

The Fisher contract met the technical specifications of the Army Corps request, the official said, and because the company’s bid was the lowest, the government was obligated to select the firm, absent a determination that Fisher had submitted an unrealistic bid.

Fisher was not among the companies the Army Corps initially selected as qualified bidders on nearly $10 billion in contracts for border barrier construction. But CEO Tommy Fisher made repeat appearances on Fox News and elsewhere to promote his company, claiming his crews could build the structure faster and for less money.

Fisher, a GOP donor, also enlisted Sen. Kevin Cramer (R-N.D.) to personally lobby the president. Cramer accused the Army Corps of treating Fisher unfairly, and at one point he stalled the confirmation of a White House budget office nominee to force military officials to provide copies of other construction firms’ contract bids.

Last month, Fisher was included for the first time in the pool of qualified eligible bidders, and the $400 million is the company’s only major border wall contract to date.

Asked about Thompson’s concerns over inappropriate influence, Cramer responded in an email: “You’d have to ask the (Army Corps) about the process.”

“It’s my understanding from General Semonite that Fisher, a prequalified builder, responded to the (request for proposals) with an acceptable design with the low bid,” he said, referring to the head of the Army Corps.

Raini Brunson, a spokesperson for the Army Corps, said in an email that the agency “will fully cooperate with a review of our contracting process.”

“The U.S. Army Corps of Engineers awards contracts in accordance with the Federal Acquisition Regulation and its supplements,” Brunson said. “Companies are awarded contracts when they are determined to provide the best value to the government for the particular procurement action being undertaken. It is not uncommon for companies that submit offers on government contracts over a period of time to provide both unsuccessful and successful offers.”

Fisher also has worked with an activist group led by former chief strategist Stephen K. Bannon and other prominent right-wing Trump supporters who are building new border barriers on private land with millions of dollars in online donations.

The group, We Build the Wall, completed a span of new barrier outside El Paso during the summer, hiring Fisher to perform the work. Chad F. Wolf, the acting homeland security secretary, visited the privately built barrier last month, and the area’s top Border Patrol official praised the structure as a “game changer.”

We Build the Wall is planning to build a new 3.5-mile span of fencing along the banks of the Rio Grande in southern Texas, on land it says Tommy Fisher purchased.

A federal judge issued a temporary restraining order Tuesday to halt Fisher’s bulldozers, siding with the National Butterfly Center, a neighboring wildlife sanctuary whose director says the project will inflict irreparable harm on the local ecosystem.

Josh Dawsey contributed to this report.