Ms Pelosi, the most powerful Democrat in Washington, was meeting with a rebel group today amid mounting calls from rank-and-file Democrats to move against Mr Trump.
So far, she has pleaded for patience, fearing any premature bid to unseat the president would be unsuccessful.
But influential party members, including Left-wing congresswoman Alexandria Ocasio-Cortez are breaking ranks.
They say it is time to launch an impeachment inquiry after the White House banned Mr Trump’s former counsel Don McGahn from testifying to the congressional judiciary committee.
Mr McGahn has been threatened with being held in contempt of Congress for failing to appear at a hearing yesterday into the Mueller report on alleged Russian interference in the 2016 election campaign.
“Our subpoenas are not optional,” committee chairman Jerry Nadler said at the start of the hearing.
“This committee will hear Mr McGahn’s testimony even if we have to go to court to secure it,” he added, before setting the stage for another clash with the White House today by issuing subpoenas to former Trump officials Hope Hicks and Annie Donaldson.
It was unclear whether ex-communications director Ms Hicks, a close confidante of Mr Trump, and Ms Donaldson, former chief-of-staff for Mr McGahn, will agree to testify as part of the committee’s probe into alleged obstruction of justice by Mr Trump.
Democrat Steve Cohen, another member of the judiciary committee, said he had drafted articles of impeachment and they are “ready to go”. But he added that without Ms Pelosi’s backing “it’s not going to happen”.
Fellow member Mary Gay Scanlon said the president “was obstructing Congress at every turn”. Ms Ocasio-Cortez said: “We now have the president actively discouraging witnesses from coming in to answer a legally-binding subpoena from Congress.”
Democrat presidential hopeful Beto O’Rourke repeated his calls for impeachment last night and said no-one should be above the law.
President Bill Clinton was impeached in 1998 over the Monica Lewinsky scandal but was cleared.