> no need to include additional threats of what you'll do after that point.
This is good advice in general, for formal communication.
Do: State what you want to happen, when, how, and why, plainly and up-front; briefly state any directly relevant and necessary information.
Do not: Hedge; express uncertainty (if they think you're wrong, that's up to them to figure out—cut the "maybe's" and the "I think"s, et c.); apologize ("sorry to bother you, but..."); threaten; whine; rant.
Request, state, and do. Do not threaten. Threatening is what you get other people to do—lawyers, elected representatives, union reps, state regulatory bodies, et c. If you threaten, you just come off like a weak blowhard. [EDIT] Take note that when those others threaten it's inherent. A lawyer doesn't have to say "or we'll sue your ass". If you are personally threatening, you don't need to threaten. It's implied. If your ordinary correspondence doesn't carry an implied threat, it's because you're not personally threatening, and you need someone who is to do it instead. That's why explicit threats from Joe Blow tend to come off as weak—the actually-threatening are threatening when they simply make requests and state their case, and if they rise to actually making a threat, it's damn scary, because it's credible. If your request isn't threatening, your threats aren't either. By avoiding weak language and not falling into the amateurish trap of leading with threats, you raise your threat level, because you come off as someone competent enough to know all this.
Concise, direct, clear language comes off as more-powerful and "higher" than wishy-washy language and threats, and it's easier to understand, besides.