(CNN) The top Democrat in the Senate, Sen. Chuck Schumer of New York, wants the Justice Department's inspector general to look into whether acting Attorney General Matt Whitaker had "unlawful or improper communications" with the White House, the latest sign Democrats are sharply scrutinizing the man leading DOJ.

"I write to request that your office conduct an investigation of whether any potentially unlawful or improper communications have occurred between Acting Attorney General Matthew Whitaker, the White House, and other entities," Schumer wrote in a letter to DOJ inspector general Michael Horowitz.

"Recent reports regarding Mr. Whitaker's unusual history of contacts with the White House give rise to serious concerns about whether he has engaged in communications intended to undermine or obstruct Special Counsel Robert Mueller's investigation into Russian interference in the 2016 election, or that otherwise may have been in violation of law or policy," Schumer wrote in his letter.

The Justice Department's inspector general's office declined to comment for this report.

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