Maybe litter producer's unchallengeable conviction (5)
I believe the answer is:
dogma
'conviction' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for dogma that I've seen before include "Doctrine laid down with authority" , "Item of belief" , "Doctrine put forward as true, not to be questioned" , "Belief, precept" , "Non-evidence based opinion" .)