If you have been treated illegally then you need to be prepared to back up your claim. Therefore, you should collect and write down as much information about the incident as possible. Who’s shift was it? Who witnessed it? What were the exact times and dates? Approach your store manager, formally in writing if you want (keep a copy of anything you send or receive). Be firm but polite and ‘business like’. Always give a timescale for them to comply and stick to it.

Here is a sample letter:

"Dear Mandy,
During David Smellypits shift on the evening of October 16th 2004, I was ordered to do the filtering by Martin Halitosis. Since the store was still open and quite busy and the protective visor could not be found, I explained that by my personal obligations under Health and Safety law I was unable to comply with his orders since I considered that doing so would present a clear and imminent danger to my self and possibly others. Martin summoned David who told me “do it now you little bastard or I’ll fry you balls”, this comment was witnessed by John Goodguy and Lucy Nicegirl. There followed an exchange of words between myself and David resulting in me being sent home. I clocked out at 8.35pm. I had been scheduled to work until 2.00am.
I am writing to you in anticipation that this matter can be resolved speedily. Firstly, I seek written confirmation that no disciplinary action will be taken against me as a result of this incident and that my record of employment will not be tarnished in any way. Secondly, I seek your assurances that both Martin and David will be retrained regarding their responsibilities under Health and Safety Law, that a new visor will be ordered and that no person will be pressured into filtering without appropriate equipment or performing other unsafe tasks. Finally, I expect financial compensation for the five hours and twenty-five minutes I was unable to work on October 16th and that my lost wages be paid in full with the rest of my earnings this pay period.
Thank you in anticipation,
A. McBeal"

Given that your manager probably has a mental age of 7, there is a good chance that they will be unable to read and will amuse themselves by building a lopsided paper aeroplane out of your letter.
Assuming the matter is not resolved at store level then you have to contact Human Resources. Human Resources are there as a safety net for the company and try to spot where they have broken the law and risk losing a court case. If you can show you have been treated illegally then human resources will appear to ‘take your side’ and the matter will be resolved. However, you should remember at all times that they are certainly not on your side and so you should be careful what you say. If they do not agree with you then they are confident they will not lose any legal dispute that results from the matter. This could be because the company did not act illegally, or because they think you do not have enough, evidence, information or determination to see the matter through.

It is very important that you follow these internal grievance procedures promptly as failure to do so negates your right to make a legal challenge in the future.

If you still think the matter is worth pursuing then you should be aware that a long and difficult process might lie ahead. It could take years of submissions before anything comes to court. However, you might want to pursue a claim to an employment tribunal and would have to submit your claim within three months of the date on which you last worked. In the example above where the worker has been pressured into filtering unsafely, he or she could claim constructive dismissal. Other claims that might be made at an employment tribunal include unfair dismissal and discrimination.
At this stage it is absolutely imperative that you consult a solicitor. Given you work for McDonalds we can assume your only option will be a solicitor offering a “no win, no fee” service. This is no bad thing- they wont take your case on unless they think you have a very good chance of winning. Of course you will be shafted for being poor again and any compensation you get will be knicked by your lawyer, but it’s the principle that counts, right?

You’re being legally screwed!?

But Shirley, but Shirley… No, they really are allowed to treat us like this. “The law, in its majestic equality, forbids the rich as well as the poor to sleep under bridges, to beg in the streets, and to steal bread” as some geezer once said. The law is designed to protect property from the majority, to protect the interests of the rich, and the interests of a certain economic system. If we have learned one thing today it is that the law is an ass and unlikely to help any of us very much.

But don’t worry about it. Just because some senile old cunt in a wig isn’t going to do anything about it doesn’t mean you can’t. Nothing ever changes unless people stand up and fight, better to get sacked on your feet than to work on your (hands and) knees.

So get involved you lazy bastard!