I did think of this possibility... So I asked several times if they were sure they did not get a travel certificate, or if they were promised something to arrive by mail. They insisted they had only gotten hotel and meal vouchers.

It was my impression that they were fully aware of what was going on (apart from the details of the merger).

But there was more to it than vouchers. They were asked to sign a document that said they had volunteered, which they did not.