That’s why in Austria we have not only Unions but a “Worker’s chamber” (and also an “Enterpreneur’s chamber”). While companies can prevent unions they can’t prevent that chamber. If you are not part of a union you can still call the chamber and it has legal specialists, it can help you and also sue on your behalf if need be, at no cost to you. If the company fires you over your legit concern’s they can also get you damages for that from that company. Of course, unions can offer stronger protection and the two institutions also work together but it is good to have a second layer that companies can’t get rid off.
These things are quite different between different countries in Europe as well though.
It just needs an employee who ended his employment in a way that was not to his or her liking. This is a huge risk for the company, the fines are substantial and huge companies will have a hard time keeping everything watertight and secret. Alternatively, hackers or other informed people can get to know a lot about the functioning of systems, firmware and software. So even if there is no one ratting the company out, they could still end up with those huge fines, or worse.