Is it me or this kind of "Easter eggs" are completely unprofessional? If you have clients then should have basic contracts, agreements, etc. Isn't this what courts are for?
At the very least it'd spark an interesting discussion with the client that might allow you to reach another measure which would satisfy both parties.
If a contract was in place for a piece of work, similar to a finance agreement on a vehicle, then legal recourse is the way to go. Be it repossession or a lawsuit.
The right answer is always have a legally binding contract :)
We do offer payment holidays and finance restructuring as to those that miss a payment.
I'll try and find it.