In a letter sent to Deputy Secretary of State Stephen Biegun Tuesday, Rep. Joaquin Castro (D-TX) said he is launching a probe into the circumstances surrounding Secretary of State Mike Pompeo’s decision to address the Republican National Convention from Jerusalem. 

Castro, the chair of the subcommittee on Oversight and Investigations on the House Foreign Affairs Committee, said Pompeo’s choice to speak at the convention “may violate the Hatch Act, government-wide regulations implementing that Act, and State Department policies,” according to Castro’s letter, which The Daily Beast obtained. The Hatch Act prohibits federal employees from participating in certain political activities. And as first reported by Politico, State documents show Pompeo’s choice to participate in the Republican National Convention may also violate legal opinions disseminated internally within the department of which the secretary himself approved.

In a cable to State employees in July, Pompeo said it was important employees “not improperly engage the Department of State in the political process, and that they adhere to the Hatch Act and Department policies in their own political activities.” In his note, Pompeo referred to a December memo from the department’s lawyers that said Senate-confirmed appointees “may not even attend a political party convention or convention-related event.”

“As the 2020 general election draws near, all Department employees are reminded to review and comply with the restrictions on political activities that apply to Department employees,” Pompeo said in his July cable.

In a statement Monday evening, Rep. Eliot Engel (D-NY), chair of the House Foreign Affairs Committee, said Pompeo’s speech “will violate legal restrictions on political activities, according to a longstanding interpretation by State Department lawyers.” Now, Castro is announcing his subcommittee’s investigation, asking Biegun to hand over documents related to Pompeo’s travel to Jerusalem, including receipts “demonstrating that any expenses incurred by the State Department were reimbursed by the RNC, Trump’s campaign, or other outside sponsors,” according to the letter. Castro is also seeking records prepared by or sent from the department’s Office of the Legal Adviser regarding restrictions on political activities by Pompeo, presidential appointees, or political appointees.

Castro also asked Biegun to provide written answers to a list of questions related to the secretary’s travel to Jerusalem and the details surrounding his RNC speech, including whether any additional legal guidance was drafted to inform Pompeo’s decision to participate in the convention. Castro gave Biegun a deadline of Sept. 10 and asked that he set a briefing time with the subcommittee by that date.

A person familiar with the matter told The Daily Beast that Pompeo’s speech was pre-recorded in Jerusalem and that the secretary will not be in Israel during its airing. The department told McClatchy that “[Pompeo’s] lawyer, the State Department lawyers, RNC lawyers, White House lawyers have all worked on his appearance to make sure it is completely lawful and appropriate.” 

The State Department has not yet made public any legal justification for Pompeo’s speech.