I faced my pressure treated wood in the run with reclaimed fence boards. They (the birds) might not get sick, but if you eat the eggs, like it says on the wood tag, you are ingesting chem. known to the state of california to cause cancer.
I would NEVER use treated lumber for something my birds come into contact with.
Treated lumber contains arsenic, to kill the insects who try to eat it. That's why it doesn't decompose. Your hens then eat the insects, ingesting the arsenic. Wanna eat their eggs?
Stick to metal t-posts, or untreated lumber.