Applicable large employers must report health coverage to the IRS each year on Forms 1094-C and 1095-C. The filings document offers of coverage and affordability and support enforcement of the employer mandate.
All three report health coverage for taxes. 1095-A comes from the ACA marketplace (needed to reconcile subsidies), 1095-B comes from insurers/small plans showing you had coverage, and 1095-C comes from large employers (50+) documenting their offer of coverage.
Forms 1094-C and 1095-C are the ACA reporting forms that applicable large employers (50+ full-time-equivalent employees) use to report the health coverage they offered. The 1095-C goes to employees and the IRS; recent law lets employers furnish 1095-Cs on request instead of automatically.