MADISON, Wis. — Democrats in the state Legislature called Monday for moderate Republicans to join them in voting against the state budget this week, and one of Wisconsin's most conservative lawmakers became the first in his party to publicly say he was casting a 'no' vote.

Democrats were pressuring Republicans in advance of the Assembly debating the $70 billion, two-year spending plan Tuesday. The Senate, where Republicans hold a narrow 18-15 majority, is expected to take up the budget on Thursday.

Republican leaders in both houses have said they don't want to make anything other than mostly technical changes to the budget, which cuts income taxes by $650 million over the next two years, allows the private school voucher program to grow statewide and rejects a federally funded expansion of Medicaid.

The budget also cuts spending in the land stewardship program, creates a private bail-bondsmen program, kicks the Center for Investigative Journalism off the University of Wisconsin-Madison campus, allows for the sale of public property and creates a new income tax deduction for families who send their children to private school.

Several of the more moderate Senate Republicans have publicly expressed their displeasure with various elements of the budget and have been working behind the scenes on possible changes to secure their 'yes' vote. None have said they would vote against the budget in its current form.

"That's why we're here, to roll out the welcome mat," said Democratic Senate Minority Leader Chris Larson at a Capitol news conference Monday. He was joined by other Democratic senators and Assembly members, state Superintendent Tony Evers and local school officials from around the state.

"My door is open to anyone who would like to change this budget," Larson said.

Republican Rep. Steve Nass, of Whitewater, became the first to pledge a vote against the budget. But his opposition alone won't mean much in the Assembly, where Republicans have a 60-39 majority.

Nass cited numerous issues Monday, including a projected $500 million deficit for the 2015-2017 budget, allowing the return of bail bondsmen and what he called a flawed voucher school expansion because income limits are too low.

Nass said he would be voting against the budget because "Republican leadership is opposed to any substantive changes in their version of the state budget and determined to block any attempts by the rank-and-file members for common sense conservative improvements."

Democrats focused largely on the voucher school expansion Monday. The budget in its current form allows private school vouchers statewide, with an enrollment cap of 1,000 students after the first year. Democrats argue those caps will be lifted and vouchers will take more funding away from public schools, which they say isn't going up as much as it should this year.

"It's a bad budget for kids. It's bad for public schools. It's bad for Wisconsin," Evers said.

Republican Sens. Dale Schultz and Rob Cowles have been the most outspoken in their desire to see changes in the budget, but several others have also spoken out about certain parts. Schultz said Monday there had been no new developments. Cowles declined to comment, saying talks were ongoing.

"I'm waiting for the Assembly to pass the budget so we can get down to having a solid discussion," Schultz said.

Republican Sen. Terry Moulton, who had earlier questioned rejecting federal money to pay for the Medicaid expansion, said he can support the budget in its current form and won't push for any changes.

"I think I can probably live with what we have," Moulton said.

Larson said Democrats were drafting several budget amendments and would work with any Republican who wants to make substantive changes, although none has approached them yet.

One way to block the Senate from making any changes would be to call a conference committee immediately after the Assembly passes the budget, a vote that's expected Wednesday. A bill passed by a conference committee, which would include Republicans and Democrats from both houses, could not be amended by the Senate.

Republican leaders in both the Senate and Assembly, who would have to agree to such a move, have denied through their spokeswomen that it's even being considered.

Larson said a conference committee bill would be insulting to the entire Senate, especially Republicans who want to change the budget.

In the budget's current form, two Senate Republicans would have to join with the 15 Democrats to have enough votes to block passage.

Once an identical budget passes both houses, it heads to Gov. Scott Walker, who has the power to make changes through his expansive line-item veto power. In 2011, when the Legislature was also controlled by Republicans, Walker issued 50 line-item vetoes.