Oppose. As Ernest (was it?) pointed out a while ago, conservatives should support the right for employers to decide whether they want their employees to be in a union or not.
I don't recall saying that, but I could have. I also support allowing secondary boycotts, but I do oppose allowing sit-down strikes in which a union holds hostage an employer's capital and other similar tactics that prevent the employer from finding other workers who are willing to work for the wages and conditions offered. I also think unions have lost a lot of their clout because a number of the functions they could do beyond simply bargaining over wages have been taken over by government and thus reduce the incentives workers have in belonging to a union.