Mostly libertarian here, but not aware of the full views of the party, so I looked it up. Apparently the 2016 election view states on unions as below which I don't see contradictory to unions. [did this for my own knowledge]

"We support the right of private employers and employees to choose whether or not to bargain with each other through a labor union. Bargaining should be free of government interference, such as compulsory arbitration or imposing an obligation to bargain." https://www.lp.org/platform/