Republican Trump tells Pelosi in a letter that her trip to Belgium, Egypt and Afghanistan, which he derided as a "public relations event," would be postponed, citing the shutdown that has entered its 27th day.
It is not clear what trip Trump was referring to. Lawmakers often do not publicize foreign trips before they occur for security reasons, particularly when the trips involve a war zone as in this case.
"Due to the shutdown, I am sorry to inform you that your trip to Brussels, Egypt and Afghanistan has been postponed," Trump's letter says.
Trump also tells Pelosi she could make the trip by flying commercial.
The US House Speaker normally uses a military plane for overseas travel and it was on that basis that Trump, as commander in chief, appeared to be acting.
Pelosi's spokesman says in response that she had planned to visit US troops in Afghanistan and receive security and intelligence briefings.
"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," Drew Hammill, Pelosi's deputy chief of staff, says on Twitter.