There's another crucial point: that this need is forecastable many (many) months in advance. If people are joining (or continuing to work at) a company with an expectation of investing in the 'long haul', but the company knows that this 'startup phase' isn't likely to last more than another nine months, there's a strong temptation for executives to deceive their employees.
As you say, 'nothing that can prevent a company to do that', but along those lines, there's nothing that prevents seeing this for what it is: an adversarial relationship where companies are doing their best to trick their employees.
Safe to say I left that place of my own accord not long after.
In periods of "low order" for things like shipping/mining a company may put the employees on leave that the government pay, but this is only temporary. It's a method to avoid hire/fire waves.
The point is that sometimes you really need less people to do the job or you can find them in other places without affecting the final product or service. There is nothing that can prevent a company to do that, not even employee friendly European legislation.