Donald Trump Jr. and former Trump campaign chairman Paul Manafort have agreed to testify privately before the Senate Judiciary Committee next week.

“Both Donald Trump, Jr. and Paul Manafort, through their attorneys, have agreed to negotiate to provide the committee with documents and be interviewed by committee members and staff prior to a public hearing,” according to a statement issued Friday evening by Judiciary Committee Chairman Chuck Grassley and Ranking Member Dianne Feinstein. “Therefore, we will not issue subpoenas for them tonight requiring their presence at Wednesday’s hearing but reserve the right to do so in the future.”

However Glenn Simpson, a founder of the firm that hired a former MI6 agent to obtain information about President Donald Trump, declined to voluntarily attend the committee’s hearing scheduled for Wednesday. The agent produced a controversial dossier containing unverified allegations that Trump had ties to Russia.

“Therefore, a subpoena has been issued to compel his attendance,” the statement said. “Simpson’s attorney has asserted that his client will invoke his Fifth Amendment rights in response to the subpoena.”