Are employer contributions tax-deductible?

For 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. For larger corporations (e.g., C-corps), employer contributions are treated as employer provided coverage for medical expenses under an accident or health plan and therefore tax-deductible.

Source: Publication 969 (2018), Health Savings Accounts and Other Tax-Favored Health Plans.