Can My Current Company Block My Employment At A New Job?

Location: California

EMPLOYMENT STATUS: Full time salaried employee

CONTEXT: I was an employee for Company A for a several years until Company A split, and spun-off Company B into a separate standalone business this year; I now work for Company B as an Independent Contributor (I'm not an executive, and do not manage anyone)

Because my current role at Company B is not the direction I want my career to go in, I found a job posting at Company A that I was interested in. I applied through Company A's job portal, went through several interviews, received and signed their offer.

I gave notice to my current manager (Company B) about my resignation. The policy at Company B is to resign w/ your direct manager, and your manager will notify HR, and HR will then update their system. Current boss has been trying to get me to stay but has been told again that I will be taking the new role at Company A; he said he would notify HR.

THE PROBLEM: I learned today that my current manager has escalated this to the CEO, who is now trying to block my move to the new job at Company A. I believe they think I was poached by Company A. Supposedly, there is a "no poaching" moratorium for one year post-companies split, but a) I haven't seen any official documentation or policies reflecting that policy and b) I wasn't poached. I saw the job on a job board and applied.

My current manager has given me no direction in terms of next steps; only notifying me about the CEO trying to block my new job. I've also learned that my current manager has told other colleagues that my resignation is "not final", but from my point of view, it is. I resigned, they just have not "accepted" it.

I've already signed my employment contract with Company A. I've spoken with my new boss at Company A about the situation and they seem confident this will work out.

MY QUESTIONS:

• Is it legal in California for my current employment to try to block my new job at Company A if I was not poached?
• What are my next best steps? I feel that I should email my current manager and HR confirming that my resignation is final, and establish my end date (two weeks from the date I first resigned to my manager)