Merritt Personal Lines Manual: Reduction of contribution limit.

You must reduce the amount that can be contributed (including any additional contribution) to your HSA by the amount of any contribution made to your Archer MSA (including employer contributions) for the year. A special rule applies to married people, discussed next, if each spouse has family coverage under an HDHP.

You must reduce the amount you, or any other person, can contribute to your HSA by the amount of any contributions made by your employer that are excludable from your income. This includes amounts contributed to your account by your employer through a cafeteria plan.