Assistant Attorney General Stephen Boyd informed the House Committee on Oversight and Reform on Wednesday that the US Department of Justice would not permit Deputy Assistant Attorney General John Gore to testify before the committee about the addition of a citizenship question on the upcoming 2020 census, defying a congressional subpoena that demanded his deposition.

In a letter obtained by CNN, Boyd states that the DOJ will not permit Gore to testify unless he is allowed to bring a department lawyer with him to the hearing. Boyd said that Gore’s defiance of the subpoena was directly ordered by Attorney General William Barr, citing executive privilege. Representative Elijah Cummings, the chairman of the Oversight Committee, has twice denied the DOJ’s request to allow Gore to bring a DOJ lawyer into the hearing, citing the longstanding prohibition against the use of counsel from executive agencies during depositions in the committee rules. The rule has been in place for more than a decade and has been maintained by both Democratic and Republican parties during their time in charge of the committee. As of Friday, the deposition has not been rescheduled.

Boyd’s letter comes as the latest salvo in the ongoing conflict between congressional Democrats and the Trump administration. Earlier this week the House Judiciary Committee subpoenaed White House counsel Donald F. McGahn II over obstruction of justice claims in the Muller report, following up its demand for the fully unredacted report a week earlier. The Trump administration has vigorously fought the Democrats’ demands, going so far as to bring a lawsuit contesting the subpoena of Trump’s tax records.