U.S. Rep. Jason Crow and six other first-term Democratic lawmakers with military and national security backgrounds say that it’s an “impeachable offense” if President Donald Trump pressured a foreign government to investigate a political opponent.

The seven House members wrote in a joint op-ed published Monday night in The Washington Post that Congress needs to scrutinize recent allegations that Trump withheld military aid to Ukraine in an effort to get the country to investigate the son of 2020 Democratic presidential candidate Joe Biden.

“These allegations are stunning, both in the national security threat they pose and the potential corruption they represent,” the lawmakers wrote.

They added: “If these allegations are true, we believe these actions represent an impeachable offense. We do not arrive at this conclusion lightly, and we call on our colleagues in Congress to consider the use of all congressional authorities available to us, including the power of ‘inherent contempt’ and impeachment hearings, to address these new allegations, find the truth and protect our national security.”

In addition to Crow, the lawmakers are U.S. Reps. Gil Cisneros of California, Chrissy Houlahan of Pennsylvania, Elaine Luria of Virginia, Mikie Sherrill of New Jersey, Elissa Slotkin of Michigan and Abigail Spanberger of Virginia. All seven unseated Republican incumbents in swing seats in last year’s election.

Crow, who defeated five-term Republican U.S. Rep. Mike Coffman in Colorado’s 6th Congressional District, called for the House to open an impeachment inquiry in late July, but before Monday’s op-ed had stopped short of supporting more aggressive moves toward impeaching Trump. The other lawmakers who penned the op-ed haven’t previously said they were open to considering impeachment.

Trump has denied he did anything improper, saying Monday there was “no quid pro quo” when he spoke in late July with Ukrainian President Volodymyr Zelensky.

The Wall Street Journal reported last week that a whistleblower complaint the Trump administration has refused to turn over to Congress alleges Trump repeatedly urged Zelensky to investigate Biden and his son, Hunter Biden, in the July conversation. The Washington Post reported Monday night that Trump personally ordered his administration to withhold almost $400 million in military aid to Ukraine at least a week before the phone call with Zelensky.

“The president of the United States may have used his position to pressure a foreign country into investigating a political opponent, and he sought to use U.S. taxpayer dollars as leverage to do it,” the seven Democratic lawmakers wrote. “He allegedly sought to use the very security assistance dollars appropriated by Congress to create stability in the world, to help root out corruption and to protect our national security interests, for his own personal gain.”

“This flagrant disregard for the law cannot stand,” they wrote, adding: “These new allegations are a threat to all we have sworn to protect.”