In Ramadge-Wonham supervisory control theory we often need to check nonconflict of plants and corresponding synthesized supervisors For a large system such a check imposes a great computational challenge because of the complexity incurred by the composition of plants and supervisors. In this paper we present a novel procedure based on automaton abstractions, which removes internal transitions of relevant automata at each step, allowing the nonconflict check to be performed on relatively small automata, even though the original product system can be fairly large. (C) 2010 Elsevier Ltd. All rights reserved.