Baker backer linked to attack ad; Spot skewered Patrick, wind farm 

A controversial radio ad attacking Governor Deval Patrick’s support for an offshore wind farm that aired during the final days of the governor’s race was funded in part with a donation from a prominent fund-raiser for Patrick’s Republican rival, Charles D. Baker.

The fund-raiser, Christopher F. Egan, was cochairman of Baker’s finance committee, according to Baker campaign materials, and personally contributed $1,500 to Baker and his running mate during the last two years, as well as $5,000 to the Republican State Committee.

The ad, which ran on five radio stations covering Greater Boston, the South Shore, and the Worcester area, was paid for by the Alliance to Protect Nantucket Sound, a nonprofit that has led the opposition to the Cape Wind proposal for nearly a decade. Egan is a former board member of the Alliance.

The Globe has reported that the ad may have breached federal tax law that bars educational and charitable organizations, known as 501(c)(3)s, from engaging in activities supporting or opposing political candidates.

Internal Revenue Service guidelines say such organizations are “absolutely prohibited from directly or indirectly participating in, or intervening in, any political campaign on behalf of (or in opposition to) any candidate for elective public office.’’ Donations to 501(c)(3)s are tax deductible because they are considered contributions to the betterment of society.

Audra Parker, the president of the alliance, has said the ad was meant to educate voters about the candidates’ views on Cape Wind and fell within the bounds of legally permissible activities. Cape Wind is planning to build 130 turbines over 24 square miles in Nantucket Sound.

“We’ve been very careful to live within the letter of the law as a 501(c)(3),’’ Parker said in a recent interview.

Egan did not returns calls to his office yesterday.

The Alliance ad initially generated controversy when Common Cause of Massachusetts, which tracks the influence of money in politics, filed a complaint with the state Office of Campaign and Political Finance, suggesting that the Alliance was required to report the expenditure and had failed to do so.

Subsequently, the Alliance reported spending more than $32,500 on the ad with money donated by Joan Hill, a California resident; Christy Mihos, a cochairman of the alliance and a two-time gubernatorial candidate; and Egan.

Greenpeace, the global environmental group, then filed complaints with the IRS and Attorney General Martha Coakley, asking for investigations into whether the alliance violated its nonprofit status by sponsoring the ad. Greenpeace filed a third complaint asking state regulators to investigate whether the Alliance should have registered as a political committee and whether the three donors violated a prohibition against coordinating political expenditures with a candidate for elective office.

Rob Gray, a top strategist for the Baker campaign, said Egan never mentioned the ad to campaign operatives.

“The Baker campaign never consulted with any entity that has to be independent about advertising,’’ he said.