A group of U.S. senators on Monday asked the U.S. Justice Department to disclose if President Donald Trump or anyone else in the White House has sought to interfere in the continuing review of the proposed $26 billion merger of T-Mobile US Inc and Sprint Corp.

The six Democratic senators, including presidential candidates Elizabeth Warren, Amy Klobuchar and Cory Booker, cited media reports that senior White House officials may be trying to influence the Justice Department’s investigation of anti-trust issues in the deal. The letter, which went out Monday, cited Trump’s reported effort to push regulators to attempt to block AT&T Inc’s acquisition of Time Warner.

“In light of the potential implications of this transaction for American consumers, we write to reiterate that the department’s decisions should be based on an impartial analysis of the facts and the law, and must be entirely free of improper political influence,” the letter said.

The White House declined to comment while Justice Department spokesman Jeremy Edwards said the review process was “free from any improper political influence.”

The deal won support from the U.S. Federal Communications Commission last month but still needs approval from the Justice Department.

The senators’ letter cited Reuters’ report last month that said the department’s antitrust division staff recommended the deal be blocked. The letter also referred to a Fox Business report that senior White House officials were supportive of the transaction.

“The prospect of department leadership ignoring a career staff recommendation to block a transaction – based on more than a year of investigation – and allowing an anticompetitive merger to proceed under pressure from the White House is deeply troubling,” the letter said.

A majority of FCC commissioners plans to vote to approve the deal after the companies agreed to sell Sprint’s prepaid brand Boost Mobile.

The final decision on whether to allow two of the four nationwide wireless carriers to merge lies with political appointees at the Justice Department, headed by antitrust division chief Makan Delrahim.

T-Mobile, whose parent company is Deutsche Telekom AG, and Sprint, which is controlled by Japan’s SoftBank Group Ltd, did not immediately comment.

In April, the White House declined Democrats’ request to disclose documents that could show whether Trump sought to intervene in the AT&T Time Warner review.

Trump, a long-time critic of AT&T unit CNN, on Monday wrote on Twitter “that if people (stopped) using or subscribing to @ATT they would be forced to make big changes at @CNN, which is dying in the ratings anyway.”

AT&T declined to comment. Its shares were up 1.1% in trading Monday.