President Donald Trump is facing pressure to cooperate with President-elect Joe Biden's team to ensure a smooth transfer of power when the new administration takes office in January.
The General Services Administration is tasked with formally recognising Biden as president-elect, which begins the transition.
But the agency's Trump-appointed administrator, Emily Murphy, has not started the process and has given no guidance on when she will do so.
That lack of clarity is fueling questions about whether Trump, who has not publicly recognised Biden's victory and has falsely claimed the election was stolen, will impede Democrats as they try to establish a government.
There is little precedent in the modern era of a president erecting such hurdles for his successor. The stakes are especially high this year because Biden will take office amid a raging pandemic, which will require a comprehensive government response.
"America's national security and economic interests depend on the federal government signaling clearly and swiftly that the United States government will respect the will of the American people and engage in a smooth and peaceful transfer of power," Jen Psaki, a Biden transition aide, tweeted Sunday.
The advisory board of the nonpartisan Center for Presidential Transition also urged the Trump administration to "immediately begin the post-election transition process and the Biden team to take full advantage of the resources available under the Presidential Transition Act."
Biden, who was elected the 46th president on Saturday, is taking steps to build a government despite questions about whether Trump will offer the traditional assistance.
He is focusing first on the virus, which has already killed nearly 240,000 Americans. Biden will announce details on Monday of a task force that will create a blueprint to attempt to bring the pandemic under control that he plans to begin implementing after assuming the presidency on Jan. 20.
Biden has already named a former surgeon general, Dr Vivek Murthy, and an ex-Food and Drug Administration commissioner, David Kessler, as co-chairs.