New York City’s unionized municipal employees and retirees enjoy some of the most expansive—and expensive—health-insurance benefits in the country. But in 2018, Obamacare’s tax on such generous plans will finally kick in, and public-sector union plans will be the first hit by the so-called Cadillac Tax. How much the penalty will amount to remains unknown, but one thing’s for sure: New Yorkers will wind up footing the bill.