Sorry, Alexandraa, you are confusing union agreements with Flight Time Limitations, which are worlds apart.
For example, I once did a rostered 4 day PHX, back to back with a 3 day BOM. When I arrived at LHR, after the BOM, I was force-drafted to do a JFK the next day. All perfectly legal, within FTLs. That's 10 days, and 3 trips, going in different directions, and I'm a pilot, so my FTLs are more limiting than CC's.
So your claiming the need for 2 days off, legally is total rubbish. But I'm not surprised; the union probably do use the term "illegal". "Against our (totally outmoded, dinosaur) agreements", would be be closer to the truth.