Two Senate committee chairmen have requested Secret Service documents on information regarding Hunter Biden’s travels to China and Ukraine during his father Joe Biden’s tenure as vice president, they announced Thursday, just one day after President Trump was acquitted by the Senate in an impeachment trial for his own conduct in Ukraine.

Senate Finance Committee Chairman Chuck Grassley (R-Iowa) and Senate Homeland Security and Governmental Affairs Committee Chairman Ron Johnson (R-Wis.) sent a letter to Secret Service Director James Murray on Wednesday asking for “all dates and locations of travel, international and domestic, for Hunter Biden.”

The chairmen also asked for the Secret Service to “note whether his travel was on Air Force One or Two, or other government aircraft, as applicable and whether additional family members were present for each trip.”

The letter to Murray stated that the committees “are reviewing potential conflicts of interest posed by the business activities of Hunter Biden and his associates during the Obama administration, particularly with respect to his business activities in Ukraine and China.”

The senators’ letter is not the first effort to acquire information on the younger Biden’s business dealings. In late November, Senate Judiciary Committee Chairman Lindsey Graham (R-SC) sent a letter to Secretary of State Mike Pompeo requesting any documents on the vice president and his son regarding their work in Ukraine.

In the letter, Graham requested Pompeo’s assistance “in answering questions regarding allegations that Vice President Biden played a role in the termination of Prosecutor General [Viktor] Shokin in an effort to end the investigation of the company employing his son.”

The company employing his son at the time was Burisma, a corrupt Ukrainian energy company on the board of which he served during his father’s vice presidency.

Hunter was earning $50,000 a month for his board position, despite having no experience in the energy sector and not speaking Ukrainian.

At the time, Vice President Biden pushed for Ukraine to fire Shokin, which he says was because Shokin was not doing enough to fight corruption in the former Soviet republic.

At the time Shokin was fired, an already-launched investigation into Burisma became dormant.

On top of allegations from Republican lawmakers that the younger Biden was earning illicit profits from the corrupt company thanks to his father’s position, some in the GOP have argued that Shokin’s eventual firing was to protect Hunter and his employer from criminal investigation.

Both Bidens have denied any wrongdoing.

Hunter has previously stated that while he regrets joining the board because it exhibited “poor judgment,” he stood by the assertion that he had done nothing improper.

“Did I do anything improper? No, not in any way. Not in any way whatsoever,” he said during an interview with ABC News in October.