A liberal watchdog group is requesting information on whether the government paid for Housing and Urban Development Secretary Ben Carson Benjamin (Ben) Solomon CarsonBiden cannot keep letting Trump set the agenda The Hill's 12:30 Report: Trump heads to New Hampshire after renomination speech Five takeaways on GOP's norm-breaking convention MORE's trip to Phoenix this week, in an attempt to discover if the trip violated federal law.

In a Freedom of Information Act request dated Wednesday, Citizens for Responsibility and Ethics in Washington (CREW) asked HUD to provide "all records pertaining to the authorization for and payment of" Carson's trip to Phoenix. Carson joined President Trump at a campaign-style rally there on Tuesday.

The request also seeks information on who accompanied Carson on the trip, as well as on whether anyone at the agency helped him prepare his remarks at the rally.

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"The requested records would go a long way toward answering the question of the secretary’s capacity at the rally, the extent to which his participation was taxpayer-funded, and the extent to which other HUD officials assisted the secretary in making a campaign-related speech," the group said in a statement.

At the heart of CREW's request is whether Carson's appearance at Trump's rally violated the Hatch Act, a decades-old law that bars most executive branch employees, including Cabinet secretaries, from leveraging their office for a political campaign.

The law, however, doesn't prohibit such officials from appearing at campaign rallies in a personal capacity.

As he took the stage Tuesday to open for Trump, Carson was introduced as "the secretary of the U.S. Department of Housing and Urban Development," prompting speculation by some that the secretary was there in his official role.

A spokesman for HUD told ABC News Thursday that the agency does not believe Carson violated the law in appearing at the rally, noting that the agency did not pay for his expenses and that he made no mention of HUD during his speech.

"His travel and lodging were not paid for by the department. He was there in his personal capacity," HUD spokesman Jerry Brown said. "He didn't discuss HUD during the speech."