My question involves a condominium located in the State of: Massachusetts

In 06' there was a no pet rule voted into the condo association and it was made a bi-law. We moved in in 07' and in our master deed there was nothing stating this by-law or we didn't receive any other paperwork given to us from the previous owners that stated this when we bought our condo. We received a letter in 07' saying that someone complained we had a dog and we had to get rid of it, we never did. We recently just received another letter (none which are certified mail, just under our doors) and told us we had to get rid of the dog or they would bring this into a legal matter. My question is, do we have anything that we might be able to fight this with so we are able to keep our 5 lb Chihuahua? We don't want to get rid of the dog and what can the condo association do when they say make this a legal matter?

Please help!