Probably nothing. Florida employers have wide latitude in implementing rules and regulations covering employees conduct and activities. As a result, they can implement a policy such as the one mentioned without recourse.
I'm not sure what happened, but the answer above was by me. Here it is again:
Assuming your workplace doesn't fall within one of the exceptions to the statute, you have a civil remedy if you are terminated for having a firearm in your vehicle at work. They are not allowed to condition your employment on an agreement not to have a firearm in the vehicle. They aren't even supposed to ask if you have one, and can't fire you for saying you have one in your vehicle.
You can either complain to the Attorney General or you can bring a lawsuit against the employer if they've violated this statute.
I hope this helps!