Union Organization Breached Contract With Our Small Business

Our company (a S-Corp) had been providing our services for close to 12 years to a Union organization. We have never received complaints about our work, have always been honest, and supported their Union. Up until last week, we were a little over halfway through a signed contract for 5 years. They sent us an email stating they were terminating our contract immediately, as of said date, with no explanation or anything. We still have 1 year and 10 months remaining on the contract. In addition, they also turned around and solicited our employee who worked there and he accepted the job he was offered. We have a clear-cut contract and we are due 50% of the remaining term of the contract. However, they are ignoring us and will not pay. As a small business, this is devastated us. What do we do? We need to sue but have no money. Is there another place we can contact since they are a labor union who has broken a contract?