There is NO national law concerning releasing employment information It is on a state by state basis. Run a search and you will see several threads on this.
In Texas I can legally tell them anything I wish. There is a misconception that there is a broad based national law limiting the release of information, because most employers are concerned about being sued. If the information is anything but factual it leaves the employer open for civil suits. I will leave it to the lawyers here to tell you if opinions and false statements would be slander or liable.
When I am asked for information on a current or previous employee I consider why the information is being asked, and what purpose it would serve for me to release that info.
If you were a turd and a mortgage company or potential employer where you being a turd is not likely to cause a problem for the public or society, then I just gives dates and eligibility for rehire. If a LEO agency calls, rest assured we will discuss your turdness.
"Speed is fine, but accuracy is final" --Bill Jordan
Remember those who died, remember those who killed them.