McAuliffe blasted the new budget signed by Northam, saying the state had "bigger problems" if it could not find more money to invest in public schools.
Northam announced that he had signed the budget on Monday, calling the measure "great" and saying it was a "very progressive" budget.
"Virginia recently adopted a $135 billion budget," McAuliffe tweeted. "If we can’t find $2 billion to invest in our students, we've got bigger problems."
Neither Northam's office nor McAuliffe's campaign immediately responded to Fox News' request for comment.
Northam signed the multi-billion dollar budget after the Virginia General Assembly wrapped up a special session to get the measure across the finish line.
The governor said the bill "includes provisions to protect Virginians from evictions and utility shutoffs." He also said that he had asked the Biden administration to extend the National Guard’s Title 32 status for the Old Dominion "through next year at 100% of the funding."
A Title 32 order is an authorization or directive given to a governor by the president to activate or start mobilizing National Guard troops in their state.
McAuliffe is still fighting for the Democratic nomination to succeed Northam, though he is the frontrunner. If McAuliffe wins the nomination, he'll be facing off against Republican candidate Glenn Youngkin for the gubernatorial seat.