Senate Minority Leader Charles E. Schumer wants to know if the acting attorney general talked to the White House about the special counsel investigation of Russian meddling in the 2016 election.

Specifically, the New York Democrat is asking Justice Department Inspector General Michael Horowitz about contacts between Matthew G. Whitaker and other parts of the Donald Trump administration about the work of Special Counsel Robert S. Mueller III and his team.

“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. I am particularly concerned about whether Mr. Whitaker may have shared with the White House, or could share in his new role, confidential grand jury or investigative information from the Special Counsel investigation or any criminal investigation,” Schumer wrote in a letter released Tuesday.

Among the questions for the inspector general is: “Has Mr. Whitaker provided any assurance to the President, White House officials, or others regarding steps he or others may take with regard to the Special Counsel investigation, including any intention to interfere, obstruct, or refuse authorization of subpoenas or other investigative steps?”

The Schumer letter comes a day after three members of his caucus who serve on the Senate Judiciary Committee filed a federal lawsuit seeking to nullify the designation of Whitaker to be acting attorney general, alleging that since he was not confirmed by the Senate to a lower office, his installation runs afoul of the Appointments Clause.

“The U.S. Senate has not consented to Mr. Whitaker serving in any office within the federal government, let alone the highest office of the DOJ,” Democratic Sens. Richard Blumenthal, Mazie K. Hirono and Sheldon Whitehouse said in the lawsuit.

Separate from Tuesday’s letter to the Justice IG, Schumer has also backed his colleagues on that effort.

“Putting aside Mr. Whitaker’s many conflicts of interest and history of hostile comments toward the special counsel’s investigation, his appointment as acting AG is in direct violation of the Constitution’s Appointments Clause and should concern every American — regardless of party affiliation — who cares about the rule of law and justice in our country,” Schumer said in a statement.

Watch: Senate Republicans Talk Leadership Team and Special Counsel Protections