WASHINGTON—The House Committee on Oversight and Reform authorized on Wednesday a subpoena for top White House adviser Kellyanne Conway, after she failed to appear at a hearing where she was asked to testify about alleged violations of laws regarding political activity.

A government watchdog recommended earlier this month that Ms. Conway be removed from her post, citing what it called repeated violations of the Hatch Act, a law that prohibits political activity by executive-branch staff. Ms. Conway repeatedly attacked Democratic...