You say you aren't in a union and then ask for any advice..... Join A Union.
Sorry but we get this ALL THE TIME, people will not join a union, usually because they dont want to go on strike, however, going on strike isn't allways the answer, in MOST cases unions are helping with all sorts of issues, they are there to protect against the practices of many employers who exploit the workers, Especially in industries such as the food industry.
THE MORE MEMBERS A UNION HAS THE MORE ABLE IT IS TO BE CALLED A UNION, and the easier it is to get results.
Pete