The city's Campaign Finance Board cleared Mayor Bill de Blasio and his nonprofit slush funds of breaking campaign finance laws in a decision yesterday, but made clear that their unfettered collection of donations from high rollers seeking favor with the mayor goes against the spirit of those laws, and the restrictions should be tightened.

The investigation, started in February in response to a complaint from the good-government group Common Cause New York, was one of several federal, state, and local investigations into de Blasio's fundraising through the group Campaign for One New York. The organization, along with two similar nonprofits, raked in more than $4 million and promoted key elements of the mayor's policy agenda, such as universal prekindergarten and a zoning scheme to incentivize construction of below-market rate housing.

The Campaign Finance review notes that more than 95 percent of the money raised by Campaign for One New York would have been considered improper under campaign finance rules, which limit campaign contributions to $4,950 per individual. At least a dozen of the donations were in the six figures, and sources included groups with business before the city, including teacher and healthcare worker unions, and Two Trees Management, the rent-stabilization-dodging developer that needed de Blasio's sign-off for the massive Domino Sugar factory development on the Williamsburg waterfront.

"New York City’s system depends on reasonable contribution limits that reduce the appearance that influence can be bought or sold through campaign contributions," board chairwoman Rose Gill Hearn said in a statement. "It defies common sense that limits that work so well during the campaign should be set aside once the candidate has assumed elected office."

The nonprofits' marketing campaigns were funneled through highly paid consultants who worked on de Blasio's campaign, and some of whom the mayor now claims are so integral to the working of his administration that they should legally be considered "agents of the city" exempt from public records laws. The board found that because the nonprofits were formed after de Blasio's election, and because Campaign for One New York claims to have stopped operating, they cannot technically be considered committees working for de Blasio's reelection, which would subject them to campaign finance rules. The board said in its decision that it will keep an eye on the groups and the campaign to see if material such as phone lists and polls compiled by the nonprofits are used during next year's reelection bid.

In a statement, Common Cause director Susan Lerner called the decision not to penalize the Campaign for One New York for raising "massive amounts of dark money" "disappointing."

"It is, however, gratifying that the CFB did make clear that politically linked 501c(4) organizations such as the Campaign for One New York must be held to stricter standards in order to ensure that dark money is not influencing government and out elections," she said. "The City Council should immediately take up legislation to strictly limit fundraising for organizations tied to elected officials such as the Campaign for One New York."

De Blasio spokesman Eric Phillips sidestepped the New York Times's questions about the mayor's support of the kind of rule-change the board and Common Cause are calling for, but said the mayor is a "lifelong advocate" for campaign finance reform. "He looks forward to continuing the work to help get big money out of politics and to make sure everyone is playing by the same rules," Phillips said.

In a supplementary advisory opinion, the board laid out its interpretation of existing rules, which it takes to mean that any group coordinating with a political candidate in the run-up to an election will be treated as part of the campaign subject to finance limits.

"The Campaign for One New York was formed to advocate for New York City’s progressive policy agenda," de Blasio campaign treasurer and Campaign for One New York spokesman Dan Leviatn said in a statement. "It never engaged in any election campaign activity for any candidate and shut down more than a year and a half before next year’s election."

Elsewhere on Wednesday, lawyers for de Blasio sought to keep secret information about the Campaign for One New York that is being sought by state ethics investigators. The Joint Commission on Public Ethics is investigating the nonprofit to see whether it lobbied officials without registering as a lobbyist in 2015.

"Lobbying is different from advocacy," Lawrence Mandelker told a state Supreme Court judge in Albany. "It sounds like everybody else is investigating the mayor and they don’t want to be left behind. That’s what it sounds like to me."

A judge is supposed to rule on whether the subpoena is valid later in the summer. The FBI, Manhattan District Attorney's Office, and other entities are also investigating the mayor's fundraising.

Last week, the FBI questioned an unemployed Brooklyn woman who had admitted to the New York Post to being a straw donor for the owner of the Inwood nightclub La Marina. Making a donation in someone else's name is a misdemeanor under state law.

A separate Post review, of de Blasio's largest contribution this year from a campaign bundler, found fishiness in the $68,750 rounded up by WeWork executive Arana Harkan from 16 donors. One donor the tabloid called said he had "no idea" how he came to be listed as a donor, and another said that he had served as a straw donor for a colleague.