The head of the Office of Government Ethics expressed alarm Saturday that the Senate would begin considering President-elect Donald Trump’s nominees for cabinet positions before they’ve been fully vetted for conflicts of interests.

“As OGE’s Director, the announced hearing schedule for several nominees who have not completed the ethics review process is of great concern to me,” wrote OGE director Walter Shaub Jr. in a letter to Sens. Chuck Schumer (D-N.Y.) and Elizabeth Warren (D-Mass.).

“This schedule has created undue pressure on OGE’s staff and agency ethics officials to rush through these important reviews,” he added. “More significantly, it has left some of the nominees with potentially unknown or unresolved ethics issues shortly before their scheduled hearings.”

The letter comes ahead of a week in which there will be a flurry of hearings for Trump’s cabinet picks. There will be hearings on six nominees on Wednesday alone.

Trump himself faces numerous questions about his business ties and extensive potential conflicts of interest. He refused to release his tax returns during the presidential campaign and has continued to do so even after winning the presidency.

Shaub wrote that he was unaware of an instance in the four decades OGE has existed in which potential cabinet picks had gone before the Senate before being fully vetted.

“This normally intensive process has been further complicated by both the Senate hearing schedule and the announcement of nominees prior to consulting OGE for an evaluation of any ethics issues. In the past, the ethics work was fully completed prior to the announcement of nominees in the overwhelming majority of cases,” he wrote.

In a Saturday statement, Schumer said the letter “makes crystal clear that the transition team’s collusion with Senate Republicans to jam through these Cabinet nominees before they’ve been thoroughly vetted is unprecedented.”

OGE emails that MSNBC obtained through a public records request showed that the ethics office had lost contact with Trump after repeatedly trying to contact them in November. The emails showed Shaub warning Trump transition officials that they were risking embarrassing the president-elect by announcing cabinet picks before notifying OGE. Without receiving guidance, White House staff could also violate conflict of interest laws.

Officials at the OGE also warned the transition team they needed to consult with the office before putting assets in a blind trust and that it could block such an arrangement if the office did not feel the trustees were truly “independent.”

Trump is expected to hold a press conference Wednesday to detail how he would resolve his business ties.

You can read Shaub’s full letter here: