If we go backwards, we see that the last postal strike that actually occurred was in 2011. That was a rotating strike, and ended up being a lockout very quickly thereafter, and then legislation by the government of the day. Prior to that, I think it was 1999. Prior to that, unless I missed one, it was 1987, which was a rotating strike and then legislation.
On October 21st, 2016. See this statement in context.