In our Canadian Reformed heritage there is a long history of opposition to labour unions. To tell the truth, this opposition has not always been consistent across the board. In some churches, church discipline was implemented with members who belonged to labour unions. In other churches, consistory members have not only belonged to labour unions, but have even held leadership positions in them. In what follows, I would like to briefly outline some important elements to consider in our thinking about this subject. There is a lot more that could be said, but in the interests of brevity I will focus on these two or three elements.
Labour unions exist to represent the interests of workers. They will stand up for their brothers and sisters against management. The typical labour union exists with the premise of an adversarial relationship between management and labour. This model derives from communist ideology where such conflict is inevitable and even desirable. As Christians, we must find such a model detestable, since God wills for us to be show love, honour, and faithfulness to those over us (including employers) and to be patient with their weaknesses and shortcomings (see 1 Peter 2:18).
Typically labour unions also require their members to swear or sign oaths of unconditional allegiance. Members promise to put the interests of the union above and before everyone and everything else. Thus, if the union votes to go on strike, the members are obligated to strike. Christians cannot in good conscience swear such oaths. They cannot vow to put the interests of the union above their commitment to God. Nor can they promise to use techniques of intimidation and confrontation should the union so decide. This conflicts with our commitment to live in peace, love, and harmony with our neighbours – including our employers (see Romans 12:18 and Hebrews 12:14).
Many Canadian Reformed Church members have worked in unionized environments, but have opted out of the labour union. In some instances, this required some kind of adjudication at a provincial labour board. Office bearers are always willing and ready to help church members prepare for such investigations, should the need arise. Opting out of the union usually will require union fees be directed elsewhere to a mutually agreed upon charity.
Finally, the above applies generally to labour unions in Canada. There may be exceptions and thus we cannot absolutely forbid membership in labour unions. However, believers in unionized workplaces have a personal responsibility to familiarize themselves with the collective agreement of the union, as well as membership oaths and requirements. You may also want to investigate the sorts of social and political causes that the union in question supports through the membership dues. Considering those factors in most instances will lead a conscientious believer to conclude that union membership is incompatible with faith in Christ.
For further reading: see chapter 8 of W. Pouwelse, A Spiritual House (Winnipeg: Premier, 1986).