The House select committee investigating the January 6 attack on the Capitol is expected to issue letters requesting voluntary cooperation from House minority leader Kevin McCarthy and around a dozen other Republican members of Congress, according to two sources familiar with the matter.

The panel intends to issue a letter to McCarthy – the top House Republican – and is considering further letters to Scott Perry, Jim Jordan, Marjorie Taylor Greene, Mo Brooks, Lauren Boebert, Andy Biggs, as well as some Republican senators, the sources said.

Congressman Bennie Thompson, the chair of the select committee, is expected to authorize the list of Republican members of Congress caught up in the investigation potentially as soon as this week. The letters may come either this week or next week, the sources said.

The scope and subjects of the letters are not yet finalized, and the sources cautioned that the members of Congress approached for cooperation may still change. On Thursday, Thompson said only that he would send letters to McCarthy and other Republicans.

But the select committee’s move to seek cooperation from some of Donald Trump’s fiercest defenders on Capitol Hill – and for some members like McCarthy, Jordan and Perry, the second such request – marks a new gear for the inquiry as it reaches its final stages.

The new letters are being discussed internally as a final chance for cooperation before the select committee considers ways to compel their assistance, the sources said: once reluctant to pursue subpoenas against members of Congress, the mood on panel is changing.

The panel has a renewed interest in McCarthy’s cooperation after new reporting this week showed he had told the Republican leadership days after January 6 that Trump admitted to him at least partial responsibility for the Capitol attack, the sources said.

The select committee is particularly focused on whether Trump might have indicated to McCarthy why he believed he was culpable for the Capitol attack, the sources said, and whether the former president knew he may have acted unlawfully on January 6.

Thompson is also considering letters to Greene and Perry and other Republicans who played an outsize role in the effort to overturn the results of the 2020 election and pressed the White House about Trump declaring martial law to stay in office, the sources said.

The select committee wants to learn more information from members of Congress who were in constant text-messages communication with Trump’s former White House chief of staff Mark Meadows, described by one of the sources as “those in the text message traffic”.

A spokesman for the select committee declined to comment.

Greene messaged Meadows on 17 January, according to one of more than 2,000 texts Meadows turned over to the investigation and obtained by CNN, that some members of Congress were calling for Trump to impose martial law to remain in power.

“In our private chat with only Members several are saying the only way to save our Republic is for Trump to call Marshall [sic] law,” Greene said in the text. “I just wanted you to tell him. They stole this election. We all know. They will destroy our country next.”

Meadows did not appear to respond to Greene’s text. But the messages Trump’s top White House aide was receiving shows the extraordinary ideas swirling around Trump after he and his operatives were unable to stop the certification of Biden’s election win on January 6.

The newly-released text messages also show Perry, now the chairman of the ultra-conservative House freedom caucus, lobbying Meadows to replace the justice department leadership with Jeffrey Clark, a DoJ official sympathetic to Trump’s effort to undo the 2020 election.

Greene and Clark were among the leading Republicans determined to overturn Trump’s defeat to Biden, according to the text messages – as well as testimony provided to House investigators by Cassidy Hutchinson, a Trump White House aide who worked for Meadows.

The select committee appears to believe the time is right to request voluntary cooperation from the members, the sources said, capitalizing on the public outrage surrounding McCarthy’s remarks and the texts sent by the Republican members of Congress.

Thompson on Thursday confirmed to reporters that he would certainly issue a second letter to McCarthy to appear before House investigators, as well as to Jordan and Perry, but declined to name other targets or how he would proceed if the requests were rejected.