Chicago Mayor Rahm Emanuel is heading to court against a Millennium Park restaurant that gets a bargain deal for a prime location.

In 2003, the Chicago Park District signed the 20-year deal that gave the Park Grill free utilities and freedom from property taxes. Now the city, claiming it and not the park district has rights to Millennium Park, wants a judge to invalidate the deal.

Michael Shakman, lawyer for the restaurant company, said his clients had been open to renegotiations, but the city was being “very greedy and unreasonable.”

“The notion that the city comes along years later, after the Park Grill turns out to be a money-making venture and says, ‘We want some of it. And we want to change the deal we made with you,’ that’s really unjustified,” Shakman said Thursday evening.

The Chicago Sun-Times editorial board once said the restaurant, “managed and owned by a block party of Mayor Daley’s friends and neighbors,” “shafts the taxpayer.”

The city’s complaint, filed Thursday in Cook County Court, also makes that latter point, though less colorfully. “The Concession Agreement does not meet commercially reasonable standards and has curtailed a potentially significant source of revenue for the city and its residents,” the city claimed.

The legal action was timed to prevent the sale of Park Grill from its original owner, Millennium Park Joint Venture, to Levy Restaurants. That deal, struck last spring, had been delayed by the Park District’s refusal to sign off on the transfer.

But, in a letter to the park district last week, Millennium Park Joint Venture said they were moving ahead anyway, as the park district had “unreasobaly [withheld] its consent,” in violation of the contract.

“We believe these facilities belong to the city,” Chicago’s top lawyer, Steve Patton, said in a statement. “And we are enforcing the city’s right to utilize them in a way that provides the fullest benefits for taxpayers.”