I've been through this in one church.

There is no national definition of "Flame Retardant" and codes vary from location to location. Ask the Fire Inspector for a copy of the local code specifying the standard they are using. Ask them for the specific remedy they will accept -and make sure it matches the code, and isn't simply the product of an overly zealous inspector "winging it". They can't just say "you can't have that hanging there" (unless of course it's hanging by a sprinkler, heat source, or emergency feature). Also ask them for advice on acceptable fabrics and treatments.

Re: Flame retardants...

You can buy spray on retardant, or you can mix powder and soak your fabric. It's not hard to do. Just remember to save the can/mix to show the inspector the next time they roll through.

Some fabrics at the fabric store come with a rating. Ask.