The email is well designed and, at first glance, does seem like it might be legitimate, but the threatening tone and the lousy spelling should make recipients suspicious.
Still, there are always inexperienced users that can be tricked into clicking on the "Print the invoice" link. Those that do will be taken to a website from which the INVOICE_FORM.zip file (containing an executable of the same name) will be downloaded.
Unfortunately, the file is not a form, but a downloader Trojan that is currently detected by less than half of the AV solutions used by VirusTotal.
By subscribing to our early morning news update, you will receive a daily digest of the latest security news published on Help Net Security.
With over 500 issues so far, reading our newsletter every Monday morning will keep you up-to-date with security risks out there.