we need to set a precedent for this kind of situation, sorry it has to be you.
You used the food allowance -- so that's kind of bizarre. (If I'm reading MO law correctly, OT is required for more than 40 hours per week/not 8 hours per day; lunches aren't required.).
They set up a policy after the fact, you agreed to it. But now they are backpedaling using THIS as the reason. Has everyone signed this "policy," or just you?
Is there any other reason why you might be considered a "precedent" for a policy that didn't exist involving specifics apparently not required by State law? Age, race, etc?
You probably haven't much of a case insofar as termination is concerned, but I'd talk with an attorney anyway.
And, if this policy may be applied to a couple of weeks prior as reason to terminate, I'd especially talk with wage and hour to find what the SOL is in Missouri for an OT wage claim. I think you can go back three years.
Department of Labor helps people to make past employers great mounds of leaves in which to wipe off shoes when employees are forced to step in ... dog stuff.