ALBANY -- New York's powerful teachers union on Wednesday withheld its endorsement and support from 38 senators who voted for Gov. David Paterson's proposal to cap the growth of school taxes, which are among the nation's highest.

NYSUT put pressure on lawmakers by saying the endorsement could still be made if the lawmakers flip-flop. NYSUT will review its decisions after Tuesday's special session of the Legislature called by Paterson, if the tax cap proposal comes up, or any time before Election Day.

"This is perhaps the most critical issue facing public education in a generation," said NYSUT Executive Vice President Alan B. Lubin in announcing what he called the suspension of endorsements. "NYSUT members are property taxpayers, too, and they, too, want relief, but not at the expense of their schools and school children."

NYSUT President Richard C. Iannuzzi said politicians supporting Paterson's tax cap chose "political expediency over the future of New York's children and public schools."

On Wednesday, the Working Families Party announced it would send 200,000 pieces of direct mail to voters with the repeated message pictured on a blackboard: "Governor Paterson's tax cap scheme will hurt our schools."

The chairman of Paterson's tax relief commission that proposed the cap, Nassau County Executive Thomas Suozzi, accused the education and labor coalition of personally attacking Paterson, a popular Democrat now in his fifth month on the job.

"Tell Governor Paterson don't hurt our school,'" Suozzi said, paraphrasing one of the ads, "I think that's personal."

Dan Cantor of the Working Families Party denied any attack on Paterson, but said criticism is focused on his "gimmick."

Losing the endorsement, votes and campaign support from local teachers -- and campaign funding from NYSUT -- could be a blow to incumbents. Senate Republicans face the possible loss of their one-vote majority in the fall elections.

Assembly Democrats are expected to meet in Manhattan Thursday to discuss an array of deals that could come together for action in Tuesday's special session. Among the issues are the tax cap and the Democrats' proposal to provide more money to help low- and moderate-income families pay heating bills this winter.

The groups favor the Assembly Democrats' proposal for a "circuit breaker." That would give breaks to elderly and middle class homeowners by basing school taxes on income, rather than their homes' market value. State aid could be added to make sure schools don't lose traditional gains in funding.

"You will give a perverse incentive for the school district to spend more money," Suozzi said, saying those not included in the break will pay more, along with businesses. "New York is No. 1 in taxes and in some cases No. 34 in test scores. So something is backwards here."

About 70 percent of school aid goes to salaries and benefits.

"We may look back at this as a significant event and significant miscalculation on their part," E.J. McMahon, from the fiscally conservative Empire Center for New York State Policy, said of NYSUT. "This is a Legislature that has been bending over backward for NYSUT for decades," McMahon said. "Do they really intend to declare war on 38 senators who, odds are, are going to be returned to the Senate?"

NYSUT had a close relationship with longtime Senate Republican Majority Leader Joseph Bruno, who retired in July. Bruno wouldn't even let Paterson's bill get a floor debate.