Well, this part is wrong. Once they become aware of the contract, they risk the potential of liability for tortious interference. [0]
> And if the former employer contacted the new one, making legal threats in order to get a person fired, isn't that itself illegal?
So long as there was no misrepresentation involved, I don't see how it would be illegal. What law do you think would be broken?
[0] https://www.law.cornell.edu/wex/intentional_interference_wit...
"The two companies were involved in a brief legal dispute last year after Nortel announced it had chosen Motorola's former chief operating officer, Mike Zafirovski, as its next CEO. Citing non-compete agreements, Motorola sued Zafirovski in October. The dispute was settled a few days later when Nortel agreed to pay $11.5 million to end the matter.
Under the terms of that October settlement, Zafirovski and Nortel agreed not to recruit Motorola employees."
(Not trying to say this case is anything like that of a much lower-level journalist as described in the article. That seems unfair and harsh)
http://www.infoworld.com/article/2674269/networking/nortel-a...
If you're a programmer, it means that you cannot work for a certain client, or even in a certain branch, but this case is so much broader.