Mandating benefits for employees imposes costs on employment. The would-be worker bears the cost. It makes the worker more expensive to hire. The employer has to pay not only a salary but also a benefit. If you make it more expensive to hire people, fewer people will be hired.
It is no different from eggs at the supermarket. If they are $2 each, you will purchase fewer of them — you will economize. This is nothing but the law of demand: consumers will demand less of a good at a higher price than of a good at a lower price. A salary plus benefits amounts to a price that the employer must pay to purchase the work of a laborer. At a higher price, less work will be purchased by the employer. FULL ARTICLE