Plans for George Lucas to build a museum in Chicago may not be as simple as once thought after a campaign group for open space threatened a lawsuit against the Star Wars creator.

Open space advocates have vowed to file a lawsuit against Lucas over the Lucas Museum of Narrative Art, which they claim would breach regulations implemented to protect open space adjacent to Lake Michigan.

Pending approval by the Chicago Plan Commission, Lucas' 95,000sq ft (8,825sq m) institution will be built on what are now parking lots between Soldier Field and McCormick Place. Architectural renderings will be presented to city officials in late September/early October, according to a statement from the museum.

The museum will house a collection that includes examples of the Star Wars special effects pioneered by Lucas and memorabilia such as the original Darth Vader costume.

A number of American football fans, particularly Chicago Bears followers who like to tailgate in the proposed area, are also opposing the plans for the museum, which is due to open in 2018.

The city's mayor, Rahm Emanuel, reportedly shrugged off the lawsuit at a recent press conference, stating: "Our contribution is two parking lots," while noting the economic and employment benefits the institute would bring to Chicago.