House Democrats are attempting to make arrangements for two of special counsel Robert Mueller’s deputies to appear for a private, closed-door testimony on the same day that Mueller is set to testify — July 17.

But the Justice Department has reportedly instructed the two special counsel staffers, James Quarles and Aaron Zebley, not to appear.

According to new reports in the New York Times and the Wall Street Journal, The DOJ’s interference could muddy the deal that the department and lawmakers reached last month to get Mueller’s testimony.

While both former Mueller associates are no longer in the special counsel’s office — and the DOJ may not actually be able to block their testimony — Attorney General William Barr already threatened in an interview with the Associated Press earlier this week that he would step in to resist any subpoena aimed at Mueller’s deputies.