The letter also reveals travel plans, including a visit to a war zone, for person who is second in line to presidency.
Congress members who were supposed to travel with Pelosi had boarded a bus outside a House office building.
President Trump previously announced he would not attend.
"The purpose of the trip was to express appreciation & thanks to our men & women in uniform for their service & dedication, & to obtain critical national security & intelligence briefings from those on the front lines."
"We're not going to allow to the president of the United States to tell the Congress it can't fulfill its oversight responsibilities ... whether our government is open or closed. That work must go on."
(corrects: irresponsible)