Legal Question in Securities Law in California

There certainly isn't any generally-applicable securities-law restriction. In rare instances, you might be deemed to be involved in "insider trading" if you have access to important news before it's made public. Sounds, however, that you don't. It may be contrary to company policy, but I don't really understand why that might be; most employers are delighted when their employees want to become co-owners, in a small way, of the firm. I think you should ask HR for some cogent explanation, and maybe go higher up. Also if there is an employee handbook, see if it sheds any light on the matter.