House Democratic leaders saw their early plans for the fall legislative session grow to a standstill Monday just hours after returning from summer break.

Democrats are trying to muscle President Joe Biden's multitrillion-dollar budget blueprint over a key legislative hurdle, but voting came to a standstill as they worked past midnight into early Tuesday to ease a standoff with a band of moderate lawmakers threatening to withhold their support for the $3.5 trillion plan.

The moderates are demanding the House first approve Biden's $1 trillion public works and infrastructure package that's already passed the Senate.

"Right now, we have an opportunity to pass something so substantial for our country, so transformative we haven't seen anything like it," House Speaker Nancy Pelosi said, according to the Associated Press.

Pelosi's leadership had sought to sidestep the issue by persuading lawmakers to take a procedural vote to simply start the process and save the policy fight for the months ahead when they will be crafting and debating details within the full $3.5 trillion budget proposal.

The standoff risks upending Biden's agenda.

Shortly after midnight, leaders announced that no further votes would be taken until Tuesday's session.