Senate Minority Leader Chuck Schumer (D-NY) on Tuesday called for an investigation into reports that federal prosecutors plan to reverse their recommended prison sentence for President Donald Trump’s friend and adviser Roger Stone.

“This situation has all the indicia of improper political interference in a criminal prosecution,” the senator wrote in a letter to Justice Department Inspector General Michael Horowitz Tuesday.

“I therefore request that you immediately investigate this matter to determine how and why the Stone sentencing recommendations were countermanded, which Justice Department officials made this decision, and which White House officials were involved.”

Stone in November was found guilty of all seven counts against him, including obstruction, false statements, and witness tampering. Prosecutors on Monday recommended up to nine years’ imprisonment for Stone, but after an angry tweet from Trump, several outlets reported that the Justice Department would scale back its sentencing recommendation.

Former prosecutors told TPM they were stunned by the development, and two career prosecutors on the Stone case, Aaron Zelinsky and Jonathan Kravis, informed the court Tuesday that they were withdrawing from the case and leaving their positions at the U.S. Attorney’s Office for the District of Columbia. (Zelinsky remains an assistant U.S. attorney in Baltimore.)

Schumer on Tuesday urged Horowitz “to conduct an expedited review of this urgent matter and issue a public report with your findings and recommendations as soon as possible.”

This post has been updated.