One part of the letter says, "your position has no basis in law, IRC bla bla bla" which of course is not true law.

So I wonder if it's a matter of passing the "hot potato" back to them with a rebuttal letter?

And the word "may" as in "may file a bla bla bla against you" seems to imply a possibility, but no real commitment, like the obnoxious yapping neighborhood dog that barks at every little thing but never attacks, never catches the squirrel, etc..