Pontiac G6 GT brake lights always on?

My Pontiac G6 GT has developed a fairly serious problem. Whenever cruising down the road, accelerating, or idling in neutral the brakes lights will come on. Tapping the brake pedal will make them go out for a bit but then they will come back on.

Does anyone know a possible cause or a solution for this? I will take the car to the dealership tomorrow but if I can fix it myself it will be better than wasting time at the dealership.