Senate Minority Leader Chuck Schumer is asking federal investigators to probe why the Trump administration postponed recreating the $20 bill with abolitionist Harriet Tubman on it.

The New York Democrat sent a letter to the inspector general of the Treasury Department on Wednesday, asking investigators to look into why the department canceled plans to replace former President Andrew Jackson on the $20 note in 2020.

The Treasury has pushed back updating the bill until 2028.

"We do not know the real reason for these decisions, but we do know that during his campaign, President Trump referred to efforts to replace President Jackson's likeness on the front of the $20 note as 'pure political correctness,'" Schumer wrote.

Treasury Secretary Steven Mnuchin has blamed the delay on ensuring that anti-counterfeiting measures and standards are being met in the new bill’s design. The $20 bill is one of the most widely circulated of all U.S. currencies and requires a strict security review.

"The suggestion that this process is being stalled is completely erroneous," Mnuchin said.

Schumer appeared skeptical of Mnuchin’s explanation.

"If the Empire State Building could be completed in 13 months almost 100 years ago, the 21st-century Treasury Department ought to be able to get this job done in a reasonable period of time," Schumer wrote.

Plans to insert Tubman, famous for leading escaped slaves out of the pre-Civil War South, on the bill have been ongoing since 2016.