He's fought City Hall in the court of law. Now he plans to fight it in the court of public opinion.

Before a small gathering of 30 supporters, businessman Kevin McCrea last week officially kicked off his campaign to unseat Mayor Thomas Menino. McCrea is also locked in a legal battle with the City Council, accusing the panel of breaking the Open Meeting law and gathering in secret.

McCrea's entry into the race was followed later in the week by City Councillor At-Large Michael Flaherty, who announced his candidacy with a letter to supporters and a video on the popular website YouTube.

At the St. Mark's Road home of Kevin Barry and Barry Mullen, McCrea, a Brighton native who now lives in the South End, called for "change" in the city.

While many eyes are turning to councillor at-large seats - numbering at two open seats if Councillor Sam Yoon also decides to run for mayor - McCrea said the city's "strong mayor" structure compelled him to shoot for the higher office.

"A city councillor can't get a lot of things done," he said. "We can't afford to let another generation of kids go to failing schools."

McCrea said he would start fundraising "like crazy" over the next several weeks, as his company, Wabash Construction, finishes up its final project, which he declined to name. He said he would be running for mayor "full-time."

McCrea pledged to end school busing, create a green science and technology exam school, and increase competition in city contracts. He also said he would push for a 12 to 1 student to teacher ratio in the schools. Putting the city's expenses online is another goal, McCrea said.

McCrea focused most of his fire on Menino, saying Menino is proposing a 5.4 percent increase in the city budget and there is no $140 million shortfall. Instead, it's just a "ploy to increase taxes," McCrea said.

Menino aides said the mayor has been upfront about the shortfall, expected to occur because of a reduction in local aid, pegged at $49 million, and an increase in health benefits, pensions and salaries. Menino has called for city unions to agree to another wage freeze.

"It's about honest representation on what's going to happen to spending if we do nothing," said Lisa Signori, the city's budget chief.

Menino aides added that the average property tax bill has fallen under Menino for two years in a row.

After Flaherty officially announced his campaign, McCrea took to his blog &endash; electkevin.blogspot.com - to hammer him for what he called a lack of transparency.

McCrea challenged Flaherty to show up to the next hearing in Suffolk Superior Court over the Open Meeting lawsuit. That's scheduled for Feb. 24 at 2 pm.

"While I have been fighting for nearly four years for transparency on behalf of the citizens of Boston, Councilor Flaherty has been fighting hard against transparency and has yet to show up once in court on this matter," McCrea wrote. "Instead, he has been hiding behind a phalanx of taxpayer paid lawyers, filing numerous motions delaying and denying the charges, spending nearly $200,000 of taxpayer money, before finally admitting guilt."

Flaherty aides said the councillor respects the ruling.

"Michael accepted the ruling and has learned from the ruling," said Jon Romano, an aide. "It's a learning experience he'll bring to his mayoral administration, where no meeting on his watch will violate the law or violate the public's trust."

Supporters of McCrea were hopeful.

"Obama was a long shot, too," said Mullen, who met McCrea in a separate lawsuit against the city to put more police on the streets. "People are listening to the underdogs."

Mullen, who helps run the neighborhood crime watch, said he was disappointed with the expected cuts to fire and public safety personnel.

"I'm disgusted with the fact that the police and fire departments are getting cut," he said. "They should've seen this coming."

Supporters who attended the Thursday night gathering included perennial candidate Althea Garrison and Back Bay activist Shirley Kressel.

More on McCrea's campaign can be found at his website.