HARRISBURG, Pa. (AP) - Pennsylvania state lawmakers returned to the Capitol for an unusual weekend session Sunday as Republicans try to advance a $29.1 billion spending plan as the clocked ticked down on the fiscal year.

The House and Senate returned to session Sunday evening, and a preliminary Senate committee vote was planned later on budget legislation whose details were just being revealed. Major floor votes on budget legislation were expected Monday, the last day of the fiscal year.

However, Gov. Tom Corbett, a Republican, has not said how he will handle budget legislation after threatening during the past two weeks not to sign it until lawmakers pass legislation that cuts future public employee pension benefits and liberalizes state laws on the sale of wine, beer and alcohol.

Under Republicans' latest budget plan, spending would increase $723 million, or 2.5 percent, over the current year's approved budget. However, another $220 million would be added to the books of the nearly-ended fiscal year, rather than the new fiscal year, making the entire package a $943 million increase, or about 3.3 percent.

The primary challenge for lawmakers is to try to fill a $1.7 billion gap in Corbett's plan torn open largely by a massive and unexpected shortfall in tax collections.

Republicans said the plan does not raise taxes, and keeps planned business taxes intact.

Democrats say that will require more than $2 billion in one-time items, including postponing bills, raiding off-budget programs and draining reserves - steps they say that merely delay the prospect of a tax increase for a year.

Democrats have proposed making up the shortfall by expanding Medicaid under the 2010 federal health care law, delaying planned tax cuts for businesses and increasing taxes on the booming natural gas industry and sales of tobacco products.

Those ideas have split House and Senate Republicans and ultimately were rejected by leaders of both. Meanwhile, Corbett has threatened not to sign a budget until lawmakers pass pension and liquor legislation.

However, Democrats have opposed GOP ideas on both fronts, and Republicans have been unable to corral enough votes from their members to get a bill on either subject to Corbett's desk.

The Republicans' budget bill would increase spending on public schools, public pensions, health care for the poor and social safety-net programs, like those for the intellectually and physically disabled.

But it pares back increases sought by Corbett in his $29.4 billion plan and Democrats complain that public schools are still suffering and the safety net is still frayed from the much-deeper cuts in aid that Republicans engineered during the past three years to balance the budget.