Those who have been called include William Stepien, who led Trump's re-election campaign, and former campaign adviser Jason Miller.
"In the days before the January 6 attack, the former president's closest allies and advisers had a campaign with misinformation about the election and planned various ways to stop the counting of electoral votes," said Bennie Thomson, chairman of the special committee.
Earlier, Trump's former chief strategist Steve Bannon, among others, was called to testify, but he refused to cooperate and never showed up.
All members of the committee have voted in favor of Bannon being held accountable for congressional defiance (equivalent to defiance of court).