Your employer cannot make you eat, however they can require you to stay on premises during short breaks. If what you're really asking is whether your employer can prohibit you from smoking during the work day, they can't do that. They can prohibit smoking on company property and in company vehicles. They can prohibit smoking around other employees to a lesser extent. They can prohibit smoking in the presence of customers or clients. They can strictly enforce time limits on breaks. The fact that you choose to slowly poison yourself is your own choice, but there are some limits to that freedom of choice.
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