HARRISBURG — Pennsylvania state lawmakers were preparing for more votes Monday as majority Republicans try to advance the $29.1 billion spending plan for the new fiscal year that begins after midnight.

A Senate floor vote was expected on the main budget bill Monday afternoon, while a House vote was expected after 8 p.m.

However, significant portions of Republicans’ budget plan remained a mystery because a large companion bill — that outlines potentially $2 billion in one-time transfers and other financial maneuvers — had not been unveiled.

Senate Republicans first began releasing details of their spending plan Sunday night, and Democrats quickly attacked the no-new-taxes proposal as inadequate for the state’s suffering public schools and built on flimsy revenue assumptions.

They also charge that the spending plan will do little to reverse deep cuts in aid to schools and safety-net programs that Republicans engineered during the past three years to balance the budget.

With lobbyists patrolling the Capitol’s corridors and lawmakers behind closed doors, the sound of a demonstration by public school advocates from Philadelphia and Pittsburgh boomed through the building. As police looked on, they crowded the hallway between the offices of House Speaker Sam Smith and House Majority Leader Mike Turzai, and chanted “Whose house? Our house!” and “Hey hey! Ho ho! This budget’s got to go!”

Senate Republicans have defended the plan as responsible and the best they could do, given a massive and unexpected collapse in tax collections that helped tear a gaping $1.7 billion hole into the $29.4 billion budget plan that Gov. Tom Corbett proposed in February.

Senate Republicans have said they were willing to cooperate with Democrats in support of a tax increase — Democrats had pressed for higher taxes on the booming natural gas drilling industry and sales of tobacco products — but House Republican leaders would not support the idea.