Thiru Vignarajah has launched a Baltimore ballot measure campaign that could scuttle MCB Real Estate’s planned redevelopment of Harborplace.

The attorney, who recently ended a publicly financed campaign for mayor by dropping out of the race to endorse Sheila Dixon, decried “a trend line across this country where developers are trying to move into our parks and privatize them for their own profit” at a Friday news conference in McKeldin Square.

His proposed charter amendment would ban residential development, buildings taller than 100 feet and other “private use inconsistent with the parks’ public nature” in the Inner Harbor and 19 other city parks. If he can gather 10,000 validated signatures from city residents by July 29, the proposal will be put to voters in the November election.

MCB Real Estate plans to demolish the run-down shopping and dining pavilions of Harborplace and replace them with four mixed-use buildings, which will include 900 apartments, restaurants and entertainment, and commercial and office space. City Hall put forward a trio of charter amendments to pave the way for the proposal. They would modify the Inner Harbor’s zoning restrictions to allow multifamily residential use, remove height restrictions and change the area’s urban renewal plan.

Vignarajah, who made opposing the Harborplace plan a key plank in his mayoral platform, said he said he wasn’t trying to prevent MCB from developing altogether. But Vignarajah’s ballot measure would block the two residential towers proposed for the new Harborplace, and project leaders have said redevelopment isn’t financially viable without the residences.

He called MCB Real Estate’s plan “a backroom deal.”

Elected officials have embraced the vision of P. David Bramble, the lead developer of MCB Real Estate, while some residents have raised concerns about design plans and the about $400 million the company is seeking in public funding.

Alexandra Hughes, a spokeswoman for MCB Real Estate, did not immediately respond to a request for comment.

City voters traditionally pass ballot measures by large margins. Asked what would happen if voters passed both his amendment and the city-sanctioned Harborplace amendments, Vignarajah said that he doesn’t believe the different measures “are in direct conflict.”

But, he added, ”there is a provision in this charter amendment that repeals and invalidates any incompatible or inconsistent provision of the city charter.”

If voters adopt two charter amendments that conflict with each other, “a court will keep as much of both as possible,” the city’s law department said in a statement. But if they’re “irreconcilable,” neither one is adopted.

State records show that Vignarajah registered a ballot issue committee with campaign finance officials earlier this month. The Protect Our Parks committee has not reported any fundraising activity.

Vignarajah and a group of organizers walked around the Inner Harbor after the news conference to start their push for 10,000 signatures. But “19 out of 20″ people they encountered weren’t Baltimore voters, said Brent Bederka, a Charles Village resident who collected about a dozen signatures in 1 1/2 hours.

Bederka said he encountered people from Baltimore County, Washington, D.C., and even New York City who were attending Fleet Week events at the Inner Harbor.

Organizers are advised to gather at least 15,000 signatures before they submit them for review to the elections board.