If you work for a typical company (e.g. C-Corp), employer contributions are tax-deductible.
If you work for yourself or have a partnership (e.g. sole proprietors, partnerships, and S-corporations), contributions to a partner’s HSA will be treated as a distribution to the partner and included in the partner’s income and may be deductible by the partner but not by the business.
Source: Publication 969 (2018), Health Savings Accounts and Other Tax-Favored Health Plans.