Please do a search here on BYC there are 100's of threads on this subject.. I must have posted a dozen times answering this question myself.
I work with cedar every day. Prolonged contact with the smell and dust of cedar is a hazard for any thing with lungs. Man and chickens alike.
A little cedar is fine, I am talking about constant contact with strong fresh cedar. (Which I can no longer smell.)
So in my coop, I mostly use shavings that are not cedar, or well aged cedar shavings that do not smell so strong any more. IMO some cedar is OK, especially if the birds can get away from it into a run or out free ranging.
So my advice is moderation, get a bag of non cedar shavings and mix them in, or dump the bag of cedar shavings outside let them air out for a few months.
ON