Maybe, maybe not. You should promptly talk to a lawyer, who can help you figure out whether you should be concerned.

Some employers have their lawyers send out such letters to employees that leave the company as a matter of course.

Some employers will threaten former employees who appear to be violating a non-compete, but then take no further action.

Some employers send such letters when they genuinely believe their business interests are at risk and are sufficiently motivated to take legal action because you appear to be violating a non-compete.

Whatever the situation – don’t ignore the letter. Contact a board-certified employment attorney. Get advice, a strategy, and some peace of mind.