Alright then, here you go: https://www.irs.gov/affordable-care-act/employers/employer-shared-responsibility-provisions
"certain employers (called applicable large employers or ALEs) must either offer minimum essential coverage that is “affordable” and that provides “minimum value” to their full-time employees (and their dependents), or potentially make an employer shared responsibility payment to the IRS."
Most places that are large enough to unionize probably would have to offer basic healthcare to their employees under the ACA already.
Small employers still have incentives to help employees with healthcare as well, just not as much as large employers: https://www.irs.gov/affordable-care-act/employers/small-business-health-care-tax-credit-and-the-shop-marketplace
"If you are a small employer, there is a tax credit that can put money in your pocket.
The small business health care tax credit benefits employers that: