WASHINGTON (Reuters) -Republican U.S. Senator Marsha Blackburn wants the CEOs of AT&T ( T ), Verizon and T-Mobile to disclose whether they received or objected to subpoenas for phone data from eight U.S. senators related to a probe of the January 6, 2021 Capitol riot, according to letters seen by Reuters on Friday.

On Monday, Senate Republicans disclosed a 2023 document that showed the FBI obtained phone data known as "toll records" from senators' phones, including Blackburn, tied to the U.S. Justice Department's investigation of the riot.

She wants the telecom companies to answer questions including whether they provided "the cell phone records of their personal devices, their official government devices, or both?"

Separately, Republican Senator Bill Hagerty -- who is among the eight lawmakers whose information was seized -- said he had written to Verizon seeking answers about the disclosure of his phone records.

Verizon on Friday told Reuters it had provided the requested customer information and call records.

"Federal law requires companies like Verizon to respond to grand jury subpoenas," Verizon said. "We received a valid subpoena and a court order to keep it confidential. We weren't told why the information was requested or what the investigation was about."

Blackburn said all three companies got subpoenas for phone records related to "time, recipient, duration, and location of calls placed on our devices from January 4, 2021, to January 7, 2021."

The records were part of special prosecutor Jack Smith's investigation into President Donald Trump's effort to overturn his loss of the 2020 election to his Democratic opponent, Joe Biden.

Trump was charged in the Capitol assault but the case did not go to trial, having been delayed and buffeted by a series of legal challenges.

Smith dropped the case after Trump won the 2024 election against Biden's Vice President Kamala Harris. Smith cited a longstanding Justice Department policy against prosecuting a sitting president, but issued a report saying the evidence he gathered would have been enough to convict Trump at trial.

Federal Communications Commission Chair Brendan Carr said Friday in an interview he had previously raised concerns about prior disclosures of lawmaker records. "We will be part of the effort to get to the bottom of what happened here," Carr said.