Chris Powell offers it in a different context, but his idea would be a brilliant defense against the ever-looming sledgehammer of litigation threats in contract disputes:

The boards that have capitulated to the lawsuit threat say it is all a matter of avoiding litigation expense. But if a board really believes that First Cathedral is so preferable as a graduation site and that the religious objection is so contrived, it could stand its ground without incurring much expense at all. For a board would not have to prove its case in court; the plaintiffs would have to prove theirs. A board could put up as elaborate a defense as it wanted, or none at all. The plaintiffs almost certainly would call school officials as witnesses anyway, and so without special expense they would have a chance to tell the court how they saw things. Maybe volunteer counsel could be found for the board. Damages seem unlikely. It’s an issue likely to come up again elsewhere, so it may be worth adjudicating.
In any event, a school board that capitulates only to avoid the expense of litigation here is advertising wimpiness, advertising that it does not have the courage of its convictions and thus inviting a lot more litigation over grievances far less serious than this one.

If it gets to the point of being a choice between capitulation and lawsuits during negotiations, seek volunteer lawyers (perhaps from a local taxpayer group) to offer the minimal defense that would procure a ruling. That way, unions bear costs and face risks when filing suits, and the elected officials do not. (Well, of course there’s always some risk, considering that judges can do just about anything, these days.)