In the US most allow but not always. For instance, NYC recently passed a law forbidding it. Many companies will not report anything other than whether or not you were an employee and the dates of your employment, but that is by their choice to limit lawsuits, frivolous or otherwise.

The idea by itself is just nuts. The employee is totally transparent while employers can hide information or just lie whenever they feel like it.

According to this USA Today story, it depends on where you live (down to the city): https://www.usatoday.com/story/money/2017/04/27/whats-your-s...

Personally, I've always been asked and it has definitely bitten me especially when moving from a region with a different cost-of-living.

As far as I know, in my state, a previous employer is only allowed to say weather or not I worked there and for how long. Nothing else should be discussed, legally. IANAL

I've only changed jobs twice in my career but I included my salary requirements in a cover letter and did not disclose my previous salary.

"Can't" is not the same as "shouldn't". Any labor attorney worth their salt will adivse their clients not to divulge more than the minimum they can get away with, but that is not the same as not being allowed to.

There are third-party services that will provide that information but only in exchange for the same information about your company (staff members, salaries, etc), and a modest fee of course.

It is very secretive though, for obvious reasons.