That is what my former manager told me when I left my previous employer. He thought highly of my skills, but couldn't write me a letter due to company policy motivated by these concerns about being sued.
The first amendment is widely interpreted to mean that you can't compel speech. Requiring a company to write recommendation letters would be compelling speech. That would be unconstitutional.
(And it doesn't matter if an individual manager would like to write a letter of recommendation but corporate policy is against it. The manager is paid by the company, would be sharing company information, and is an agent of the company in this regard.)
It would, but that's not what's being discussed.
The accusation is that the companies are restricting speech by saying that managers cannot provide a reference, even if they clearly state in said reference that the views are their own and not that of their employer. Nobody is trying to compel anyone else to provide a reference, the idea is that nobody should be prohibited from it, especially since for long term employees leaving on good terms their manager(s) is/are probably one of their best references.
A manager's evaluation of another employee's performance is internal company information. There's no reason that a company should be compelled to share that information externally.
It doesn't matter if the manager wants to share it, any more than the manager wants to share all the source code the employee has written.
Companies are allowed to determine what gets shared by their current employees, end of story. On the other hand, it is unconstitutional for the government to override that.
There are exceptions for things like public companies that are compelled to release certain data on a quarterly basis in exchange for the benefits of being publicly traded. And plenty of information can be compelled to be shared privately with the government, whether taxes or for health inspections or whatever.
But absolutely not forcing companies to allow their employees to talk publicly about other employees' performance.
This is trivial to solve: both former employer and employee sign the letter, declaring that information in it is full, correct and they have no objections. It would be much harder to sue if you previously agreed that the letter is ok for you.
Edit: and remember, this is to file a suit, not win a defamation suit, which can be difficult. However it is very expensive for an employer to defend itself, easily tens of thousands if not six figures of dollars. How the game is played is a disgruntled ex-employee files a suit and then tries to settle for low tens of thousands of dollars, a portion of which goes to the employment attorney they hired.