What caused congress to want to restrict the power of unions?

Republican congressmen aim to legislate a bill related to "the right to work". This bill aims to grant workers the option to avoid paying union fees. This is seen by the unions as a pro-business attitude from the government which aims to hinder the bargaining power of the unions, as these would face a shortage of funds for their day to day operations and affairs.

The correct answer to this open question is the following.

Republican congressmen aim to legislate a bill related to "the right to work" because they want to support businessmen instead of unions. The "right-to-work" legislation establishes that employers and unions cannot force workers to pay dues to unions in order to work. Although there would be a union in your workplace, if you do not want to be part of that union, you are free to decide to not pay anything and have no consequences for avoiding the payment. You still work as normal.