More than 400 former Department of Justice employees have signed a letter stating they are “disturbed” by President Donald Trump’s pick for acting attorney general, Matthew Whitaker, and demanding he be formally vetted by the Senate.

Published by the watchdog organization Protect Democracy, the letter features hundreds of career employees who served under both Democratic and Republican administrations, according to the group.

“Because of the profound responsibilities the position entails and the independence it requires, it can only be filled by someone who has been subjected to the strictest scrutiny under the process required by the Constitution,” the letter reads. Its signatories include former senior officials, attorneys and judges, among others.

The White House has defended Whitaker’s appointment, saying he is only serving temporarily. Yet the president is reported to feel “no urgency” in permanently filling the post, a process that requires Senate confirmation.

Whitaker took over for Attorney General Jeff Sessions at Trump’s request in early November, skipping over the obvious choice, Deputy Attorney General Rod Rosenstein.

The attorney, who formerly served as Sessions’ chief of staff, has drawn sharp criticism for publicly speaking in favor of Trump and against the special counsel investigation into Russian interference in the 2016 election. He now oversees the investigation, which has led to concerns over how he may choose to steer it. Once, Whitaker suggested the budget for the investigation be tightened to prevent it from fulfilling its mission.

“The Attorney General is responsible for ensuring that we are a nation of laws,” the letter reads, “and that every citizen and every government official  —  including the President himself  —  is equally subject to those laws.”

Whitaker faces an avalanche of opposition. Late last month, three sitting senators filed a lawsuit challenging the legitimacy of the appointment with the help of Protect Democracy and the Constitutional Accountability Center, another watchdog group. The move was followed by a request from a coalition of attorneys general from 14 states and the District of Columbia, asking a federal judge to block Whitaker’s appointment.

One attorney, Thomas Goldstein, requested help from the United States Supreme Court.