Then you go where there's a bathroom. That could be the restaurant 5-6 miles away, or back to your employer's facility, or even home.
They have at least a lawyer. While the lawyer may not talk specifically about restroom access, you can be damn sure they talk about liability. So does the insurance agent.
Different businesses have different rules. Why would the rules for two different businesses, even with identical floor plans, be even similar?

Even with the employer not wanting to get rid of the employee/looking for an excuse. Create a firable offense, get fired.