Organizers of an IndyCar race planned for South Boston over Labor Day weekend urged backers on Tuesday to sign an online petition expressing their support for the race, after an opposition group recently ramped up efforts to stop the event from coming off in the Seaport district.

In an e-mail addressed simply to “Friends,’’ John Casey, chief financial officer of Grand Prix of Boston, the group hoping to bring the race to the city, said that as the event “continues to undergo exhaustive review by multiple agencies at both the City of Boston and the state, demonstrating public support and excitement about the race at this point is critically important.’’

The petition had more than 1,000 supporters by Tuesday evening, according to the Friends of IndyCar Boston website.

The appeal read in part, “This event promises to bring a significant amount of tourism and economic benefits to the region on a weekend that is typically a down time for the industry in Boston.’’

Laurence Bishoff, cochairman of the Coalition Against IndyCar Boston, criticized the effort by Grand Prix of Boston in a phone interview.

He described the online petition as “typical of this promotional group. They’re trying to tell the city that they should run this race, and in fact all the arguments that we have made, and others have made, say it doesn’t make any sense for the race to be in the city of Boston on Labor Day weekend.’’

Bishoff’s group recently asked the state to require race promoters, the city, and state agencies working with Grand Prix to undergo an extensive environmental review of the project. That request is pending.

The opposition group contends that holding the race in the Seaport will harm the environment and cause damage from noise, traffic, construction, hazardous waste, and other factors.

In December, race promoters signed a letter of intent with representatives of several government agencies whose cooperation was needed for the event to go forward.

The agencies agreed that they intended to negotiate with promoters and enter into binding agreements for the race.

The pact also stated that Grand Prix of Boston will be responsible for costs associated with the event.

Mark Arsenault of the Globe Staff contributed to this report. Travis Andersen can be reached at travis.andersen@globe.com.