In the area that I work, a certain set of employees are automatically covered by a collective bargaining agreement, whether they pay dues to the union or not. The employer has rolled out a benefits package that includes 8 weeks of paid parental leave. There is a stipulation that says if you're covered under a CBA, you're not eligible for the benefit. The employees are given no choice of being covered under the CBA or not. Additionally , upon being hired, there isn't any information given in regards to this, or the ability to opt out.
How is this legal?