Attorney General William Barr has authorised federal prosecutors across the US to pursue "substantial allegations" of voting irregularities before the 2020 presidential election is certified, despite little evidence of fraud.
Barr's action comes days after Democrat Joe Biden defeated President Donald Trump and raises the prospect that Trump will use the Justice Department to try to challenge the outcome.
It gives prosecutors the ability to go around longstanding Justice Department policy that normally would prohibit such overt actions before the election is formally certified.
In response to Barr’s memo, Richard Pilger, the director of the US Department of Justice's Election Crimes Branch, has resigned.
"Having familiarized myself with the new policy and its ramifications ... I must regretfully resign from my role as Director of the Election Crimes Branch," Pilger's letter read, as quoted by Sputnik.
This development comes as Republicans, led by in Donald Trump has refused to accept win of President-elect Joe Biden, claiming widespread "voter fraud."
Amid Trump's refusal to concede, Attorney General Barr has issued a memorandum that authorized the federal authorities to launch inquiries into credible accusations of voting irregularities in the US presidential election.
Barr said the claims should be investigated before the results of the election are made public.
Trump has not conceded the election and is instead claiming without evidence that there has been a widespread, multi-state conspiracy by Democrats to skew the vote tally in Biden's favour.
Biden holds a sizable lead in multiple battleground states and there has been no indication of enough improperly counted or illegally cast votes that would shift the outcome.
In fact, election officials from both political parties have publicly stated the election went well, though there have been minor issues that are typical in elections, including voting machines breaking and ballots that were miscast and lost.
In a memo to US attorneys, obtained by The Associated Press, Barr wrote that investigations "may be conducted if there are clear and apparently-credible allegations of irregularities that, if true, could potentially impact the outcome of a federal election in an individual State."
States have until December 8 to resolve election disputes, including recounts and court contests over the results. Members of the Electoral College meet December 14 to finalise the outcome.