Son notificaciones que se envían al futuro (e hipotético) demandado para conseguir llegar a un acuerdo previa acción legal. Mi padre era abogado y las enviaba como política habitual para evitar entablar una demanda. Generalmente se trata de cartas en donde se solicita a la parte en falta que ponga al día su situación. A veces también pueden ser notas ofreciendo algún tipo de mediación pre-judicial.

See this:

A letter before action is just what it says. It is a letter sent notifying someone of the intention to take legal action.

Some people would say ‘don’t bother with threats, just sue ‘em’. This might sound tough but it’s really just a great way to get stuck with a heap of legal bills when your ‘victim’ points out to the judge that they would have paid up if only they had been formally warned that a court case might result. A letter before action is a lot cheaper than solicitor’s and court costs.

So what should such a letter contain?

It must be very clear that unless the issue is resolved court proceedings will result.