The board may direct the parties, their representatives or attorneys, to appear before the board, or the chairman or any member thereof, for a prehearing conference to consider the simplification of the issues and such other matters as may aid in the disposition of the appeal by the board. The board, its chairman or any member, shall make an order which recites the action taken at the conference and the agreements made by the parties as to any of the matters considered, and which limits the issues to those not disposed of by stipulation or agreement of the parties. Such order when entered controls the subsequent course of the proceeding, unless modified.