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:

• Have fewer than 25 full-time equivalent employees
• Pay average wages of less than $50,000 a year per full-time equivalent (indexed annually for inflation beginning in 2014)
• For tax year 2014, the inflation-adjusted amount is $51,000
• For tax year 2015, the inflation-adjusted amount is $52,000
• For tax year 2016, the inflation-adjusted amount is $52,000
• For tax year 2017, the inflation-adjusted amount is $53,000
• Offer a qualified health plan to its employees through a Small Business Health Options Program Marketplace (or qualify for a limited exception to this requirement)
• Pay at least 50 percent of the cost of employee-only – not family or dependent – health care coverage for each employee"