Governor Paterson is coming under increasing pressure to back down on his insistence that lawmakers approve what would be one of the most aggressive anti-tax measures in state history.

Mr. Paterson, a Democrat, surprised many earlier in the year when he expressed support for setting a strict limit on how much suburban and upstate school districts can tax their residents each year.

Legislation supported by Mr. Paterson would prohibit taxes from increasing by more than 4% a year. The idea immediately drew a rebuke from organized labor leaders, who fear such a cap would ultimately harm teachers and other school employees by forcing schools to trim their budgets and thus salaries and benefits.

Fueled by the Republican-led Senate’s passage of a tax cap on Friday, opposition to the governor’s plan has sharply intensified this week, with a coalition of labor-backed groups spending $1.5 million on an attack ad campaign that singles out Mr. Paterson for scorn.

The campaign is financed by two groups that had been allies of the governor: the Working Families Party, a labor-backed group that has played an influential role in many legislative races, and the Alliance for Quality Education, which lobbies for increases to public school aid and has ties to both the United Federation of Teachers and Citizen Action, which is funded by both labor unions and the New York trial lawyers’ association.

The 30-second spot was produced by the consulting firm Knickerbocker SKD, whose principals have ties to Senator Schumer and Attorney General Cuomo. It began airing in New York City and other large markets around the state yesterday, marking the first time Mr. Paterson has been the target of a television attack ad since he took office in March.

Mr. Paterson until now had largely avoided clashes with interest groups and organized labor as he has sought to position himself as a fiscally responsible leader. With only an Assembly vote standing in the way of passage of a cap, critics of the legislation have turned the heat on the governor days before lawmakers are to return to Albany for an emergency special session.

The governor has indicated he wants the Assembly to approve a cap during the special session and is trying to negotiate a deal with the Democratic speaker, Sheldon Silver, who has said he is wary of imposing spending limits on school districts and prefers to use state aid to lower the tax bills of homeowners.

The ad campaign is seen by Albany observers as a taste of the political consequences in store for Mr. Paterson if he pushes Mr. Silver and his conference too hard. The governor has enjoyed a growth in public support in recent weeks, with one poll showing that 64% of New Yorkers approve of his performance.

Although polls show that most New Yorkers favor a cap on property taxes, an ad campaign casting Mr. Paterson as an enemy of schoolchildren could put a damper on his popularity.

Titled “Wrong Answer,” the spot begins with an ominous tick-tock piano motif, as a male announcer intones: “Everyone agrees that property taxes are a problem. But Governor Paterson’s proposed tax cap gimmick is the wrong answer. They tried this scheme in California, Illinois, and Massachusetts and the consequences were devastating. Billions in education cuts, overcrowded classrooms, teachers fired. And Paterson’s plan won’t even cut our property taxes. Tell David Paterson hurting schools is the wrong answer.”

A slow-motion image of a stern-looking Mr. Paterson delivering his inaugural speech in the Assembly chamber is shown twice, interspersed with shots of a lonely teenager sitting in a darkened school hallway (symbolizing funding cuts), a racially diverse selection of elementary school pupils sitting in close proximity (crowded classrooms), and an attractive female teacher lecturing on long division (teacher layoffs).

Working Families Party officials say a cap on property taxes would punch holes in school budgets and would widen disparities between poorer school districts and wealthier areas whose residents they say are more likely to take advantage of a provision in the bill that allows voters to override a cap.

The Paterson administration says a cap is an effective way to force school districts to become more efficient and to encourage the Legislature to pass laws lowering education costs. New York spends more per pupil than any other state largely because of higher labor costs: teacher salaries, health benefits, and pensions.

Officials point out that the least wealthy school districts, which have a more limited tax base, have been raising property taxes at rates well below 4% each year. Those districts depend much more heavily on state aid than wealthier areas, which have raised taxes at much higher rates.

“There is widespread recognition among New Yorkers that runaway increases in property taxes are deeply hurting our state. We can’t ignore this reality as struggling residents continue to vote with their feet, leaving our state to find tax relief elsewhere,” a spokesman for the governor, Errol Cockfield, said.

“Anyone who does not acknowledge this trend is out of touch with working families. The longer we wait to approve a property tax cap, the more we will hamstring New York from reaching its full economic potential,” he said.