The “Boston Grand Prix” hit a roadblock Friday, after Boston’s Conservation Commission voted to stop Indy-car race promoters from building parts of the race course in the city.

The commission cited environmental issues in areas of the course over wetlands.

Mayor Marty Walsh has been the biggest proponent of the Grand Prix, but now he’s siding with his environmental department.

Construction can’t start until promoters get a new permit.

It will now be an uphill battle to get the course finished on time for its scheduled start on Labor Day weekend.

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