Speaker Pelosi took aim at the president and accused him of trying to “stir the pot” with his claims that votes received after election day should not be counted.
“On 20 January 2021 Joe Biden will be inaugurated president of the United States. The states will count the votes that they have in a timely fashion," Pelosi said on MSNBC.
"The easiest thing for him (Trump) to do is to stand up like a man and accept the results of an election of the American people.
"For him to make these kinds of statements shows his lack of patriotism, his undermining of our elections while he allows foreign countries like his friend Putin to undermine the integrity of our election, he himself is doing it as well.”
Observers say it is unlikely that the winner of the election will be officially named on Tuesday night with a large number of mail in ballots to be counted.
The president has attacked that process and said he wants the result to be clear on election night.
“It would be very, very proper and very nice if a winner were declared on 3 November instead of counting ballots for two weeks, which is totally inappropriate and I don’t believe that that’s by our laws,” Mr Trump said on Tuesday.
“We’ll see what happens.”
There is no law requiring states to certify their election results on election day and federal law says they have until 8 December to resolve any “controversy or contest” about appointing its electoral college electors.
Mr Trump has regularly wavered on committing to a peaceful transfer of power, a hallmark of US democracy.