A group of US senators say they will refuse to certify Joe Biden's election victory unless a commission is set up to investigate alleged voter fraud.
The 11 senators and senators-elect, led by Ted Cruz, want a 10-day delay to audit the unsubstantiated allegations.
The move is not expected to succeed as most senators are expected to endorse Mr Biden in the 6 January vote.
President Donald Trump has refused to concede, repeatedly alleging fraud without providing any evidence.
His legal efforts to overturn results have been rejected by the courts.
The US Electoral College - which confirmed November's presidential election result by awarding points for each state won by the two White House rivals - last month cemented Mr Biden's victory over Mr Trump by 306-232.
These votes must be affirmed by Congress on 6 January. Inauguration Day, when the new Democratic president and vice-president are sworn in, will be on 20 January.
In a statement, the 11 senators led by Texas senator Ted Cruz said November's election had "featured unprecedented allegations of voter fraud, violations and lax enforcement of election law, and other voting irregularities".
Citing a precedent from 1877 - when a bi-partisan committee was formed to investigate after both parties claimed victory in three states - they urged Congress to appoint a commission for an "emergency 10-day audit of election returns in the disputed states".
"Once completed, individual states would evaluate the commission's findings and could convene a special legislative session to certify a change in their vote, if needed," they said.
However they said their bid was unlikely to succeed. "We are not naïve. We fully expect most if not all Democrats, and perhaps more than a few Republicans, to vote otherwise," they said.
Their move is separate from that of Missouri Senator Josh Hawley, who has also said he will reject the Electoral College result over election integrity concerns.
A group of Republicans in the lower chamber of Congress, the House of Representatives, is also planning to contest the election results.
Source: BBC