"It will be a follow-up on the announcement yesterday to better understand voter fraud," White House press secretary Sean Spicer told reporters aboard Air Force One, as quoted by The Hill.
He said that Trump will sign an executive action to launch the probe on Thursday, according to a report by McClatchyDC.
The President announced Wednesday that he will order a "major" investigation into voter fraud.
Later the same day, Spicer told reporters that Trump's investigation will focus on "urban areas" in primarily Democratic states like New York and California.
House Oversight Committee Chair Jason Chaffetz (R-UT) said Wednesday evening he sees "no evidence" for the kind of voter fraud that Trump alleged and that his committee will not use taxpayer money to investigate the President's claims.