The leader of House Democrats, Hakeem Jeffries, said on Sunday that he will vote to impeach Defense Secretary Pete Hegseth, describing himself as "a hard yes" in an interview with ABC's This Week.
Jeffries accused Hegseth of abusing his power, damaging national security and leading the United States into a costly war with Iran.
The resolution is being brought by Thomas Massie, an outgoing Republican congressman who has often clashed with President Donald Trump. He says he will file it as early as Monday. It contains eight articles of impeachment, including a charge that Hegseth broke the War Powers Resolution of 1973, the law that limits a president's ability to wage war without approval from Congress.
A vote in the House could come this week, as lawmakers return following the midterm elections. Impeachment needs a simple majority in the House, while removing an official from office would require a two-thirds vote in the Senate.
Hegseth has rejected the accusations. In a video posted on social media, he defended the war and dismissed the articles as a sham, comparing them with the two impeachments of President Trump. Mr Trump has called Hegseth a "great warrior" and criticised the push to remove him.