I see. That sounds like a pretty lame excuse doesn't it? It indicate to me that this is an employer who is not very sophisticated with regard to the law.
Yes, it does appear you could make out a violation of law based on retaliation for filing a worker's comp claim under CA Labor Code Section 132a.
Here is a link to that section:
This appears to be a classic case of retaliation and the fact you complained to HR on at least several occasions should aid you in proving your case since there should be documentation that can be retrieved from them through the discovery process if a lawsuit is filed against them.
I would recommend retaining a local employment law attorney to represent you in this matter. It may be that a demand letter from the attorney could resolve the matter once the employer is informed of your rights and what appears to be clear violations of state law, if they wish to avoid a lawsuit.
The state and local bar associations can provide you with attorney referrals.
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