The Campaign Finance Board is recommending a series of proposals that would significantly tighten restrictions on political contributions and spending in city elections, including additional regulation of contributions by people “doing business” with the city and a ban on all donations by businesses and unions.

If implemented, the proposals would also slash contribution limits in all city campaigns and would lower the amount of public funds available to match private donations in certain races.

The board issued its recommendations yesterday as part of its official report on the 2005 city elections, which scrutinized patterns in contributions and campaign spending.

The proposals would deepen the city’s already extensive regulations on the financing of political campaigns. Supporters say the system increases opportunities and helps to level the playing field among candidates while critics charge that the restrictions hamper legitimate political activity.

Looking to target “pay to play” activity, the board urged the City Council to pass legislation regulating contributions from people “doing business” with the city. A 1998 amendment to the city charter gives the board the power to issue regulations on its own, but the board yesterday said the matter should be addressed legislatively, without specifying how. That decision drew criticism from the mayor’s office, which has pushed the Campaign Finance Board to adopt rules on its own. “We continue to urge the CFB to do that, instead of trying to punt responsibility to the City Council,” the mayor’s spokesman, Stuart Loeser, said.

The council was noncommittal yesterday. A spokesman for the speaker’s office, Anthony Hogrebe, said the council would review the board’s recommendations.

The chief challenge of adopting a “pay to play” regulation would be defining what it means to be “doing business” with the city, an attorney with the New York Public Interest Research Group, Gene Russianoff, said. The term can be narrowly applied to those with a city contract, or it could be expanded to include people who make land use applications to the city, or to an even broader definition.

Mr. Russianoff voiced support for regulation, but with limits. “If you apply for a license for a sidewalk café, do you have to register? I don’t think so,” Mr. Russianoff said. He added, “You have to draw the line somewhere.”

The “pay to play” proposal comes after the city in May enacted legislation stiffening disclosure requirements for lobbyists and barring their contributions from receiving public matching funds.

The board’s proposal to ban all “organization contributions,” including unions and LLCs, also faces opposition. A top official with the region’s largest healthcare union, Service Employees International Union Local 1199, urged the Campaign Finance Board to drop the proposed ban. “1199 represents hundreds of thousands of workers who simply cannot afford to make personal contributions to candidates,” the union’s executive vice president for politics and legislative affairs, Jennifer Cunningham, said. “To rob union members of their voice in supporting candidates they believe would represent working families is a serious injustice.”

Aiming to boost the chances of challengers over incumbents, the board also wants to take large sums of money out of City Council races by cutting the maximum contribution to $250, which would be a sharp drop from the current limit of $2,750. The proposal would also slash the spending limits in council races for those who accept matching funds and reduce the amount of publicly available matching funds.

Other recommendations include the reduction of contribution limits in citywide races to $4,000 from $4,500 and, in campaigns for borough president to $3,000 from $3,500.

The five member board is appointed by the mayor and by the speaker of the City Council. The chairman of the board is Frederick A.O. Schwarz, Jr., a lawyer at Cravath, Swaine and Moore.