I can confirm this from personal experience (at least it was the case 10 years ago).

That sounds terrible, can you elaborate?

I've read from blog posts and even from conversations that companies require acquihires, particularly non-founder employees, to go through an interview process. It may be shortened, but they still often have to do the typical algorithmic interviews.

I'll see if I can find one of the blog posts I've read about the process.

Note: to be clear, I'm describing the process for acquihires, not founders just wanting to sell their company and walk away with some cash (which actually seems to be somewhat unusual).

Edit: this was discussed in a similar thread on HN just last year: https://news.ycombinator.com/item?id=18943500

Is that a uniquely American thing? I'm 100% certain that even if the company I work for was acquired, my current contract would still apply. So I would need to be given at least 3 months notice, and couldn't be discharged without a good reason - failing some internal interview wouldn't be such a reason.

Perhaps. Most places in the US an employment contract can be terminated at will for almost any reason or without any specific reason.

Can also confirm from my own experience 3 years ago