Senate Minority Leader Charles E. Schumer asked the inspector general of the Treasury Department on Wednesday to open an investigation into the Trump administration decision not to release new $20 bills with Harriet Tubman’s portrait next year as planned.

The federal government was well into the redesign process to replace the image of President Andrew Jackson, a slaveholder, with that of Tubman, a 19th-century slave-turned-abolitionist, when Treasury Secretary Steven Mnuchin announced in May that it was being delayed until at least 2028.

Schumer (D-N.Y.), in a letter to Treasury’s watchdog, Eric Thorson, asked that the inspector general’s office review the decision to determine whether the White House influenced it. Schumer said he wanted “to ensure that political considerations have not been allowed to infect the process for designing American currency.”

He asked Thorson to look into any interagency process related to the redesign, including among the Secret Service, the Federal Reserve and the White House.

The Obama administration responded to a grass-roots effort to put Tubman on the $20 bill after a group called “Women on 20s” took a survey to determine which historical woman should replace Jackson and Tubman won. In 2016, Obama’s treasury secretary announced plans to roll out new $20 bills featuring Tubman’s likeness by 2020 to coincide with the 100th anniversary of passage of the 19th Amendment, giving women the right to vote.

Then-candidate Trump called the decision to change the face of the $20 bill “pure political correctness.” Trump has called himself a fan of Andrew Jackson. During a 2018 rally in Tennessee, Trump said, “This is the state of Davy Crockett and Andrew Jackson. Andrew Jackson, who continues to be on the $20 bill. You know that?”

Trump’s Treasury Department also removed mention of the Tubman $20 bill from its website.

Mnuchin has cited the need to take extra anti-counterfeiting measures as the reason the process is being delayed, but the New York Times reported that Mnuchin wanted to stall the change until after Trump’s presidency to avoid controversy with the president, who could have responded by scrapping the plans altogether.

“There is no reason to reverse the original decision to recognize her heroic legacy on the $20 note,” Schumer wrote. “Any unnecessary delays, especially for political reasons, in redesigning the $20 note in her honor are improper and unacceptable.”