Typical progressive response: "There is scant evidence such a letter has even been thought of and, in any event, no one is talking about mailing it out to the public."
I.e., at this point, unless you are among those the government suspects has a semi-automatic in your home, you will not receive such a letter and may never have any idea of what is transpiring until, of course, it is too late.
Those that ignore such a letter may well find liens on their various bank accounts that must be paid prior to any further withdrawals.
Didn't we see this movie when it came out in the 1930's?
Move your accounts to a free state, or disguise them under family trusts. Starve the beast, lest he cause you to have to shoot him later.