The general issues of concern are:
MISAPPROPRIATION OF EMPLOYER'S TRADE SECRETS. Claims that an employee has specialized knowledge and is using it to a former employer's detriment is actionable against the new employer and former employee.
BREACH OF COVENANT NOT TO COMPETE. Although restrictive covenants are generally void under Bus. & Prof. Code 16600, an employee who entered into an employment contract containing a restrictive covenant pursuant to the law of another jurisdiction (e.g., employee worked in NY, under contract with noncompete cluase, then moves to California) , can be held liable for the breach of covenant.
SOLICITING FORMER EMPLOYER'S CUSTOMERS. While this sort of competitive activity is also generally protected per B&P Code 16600, the misappropriation of the former employer's customer lists can be enjoined and damages awarded, as a trade secret violation.
SOLICITING FORMER EMPLOYER'S CUSTOMERS. Once again, protected by B&P Code 16600 -- however, if a former employee's contract had a fixed-termination date (employment not "at will"), then the former employer can sue the new employer for "intentional interference with contractual relations," if the employee quits the existing contract at the instigation of the new prospective employer.
Hope this helps.
NOTICE: My goal here is to educate others about the law. I am always available to answer your follow-up questions after you click Accept – however, if you do not click Accept, the website gets paid, and I receive nothing. This is true, even if you are on a subscription plan. So please click Accept, so that I will be able to continue to provide this service for others in the future.
And, if you need to contact me again, please put my user id on the title line of your question (“To Socrateaser”), and the system will send me an alert. Thanks!