There is a fairly common IRS or "tax scam" being practiced by scammers in both Canada and the USA.
USA tax payers should read this:
http://www.irs.gov/uac/Newsroom/IRS-Reiterate ... -Telephone-Scam
Short answer:
The IRS never initiates a contact via phone.
They always send a snailmail first.
Got a voice message. Poor English. Person claimed to be with the IRS: "I'm officer Hedelgrave of the Internal Revenue Service, the hotline to my position is 202-506-9864, I repeat 202-506-9864. Don't disregard this message and do return the call before we take any legal ALLEGATION against you. Goodbye and take care." This is a word for word; as noted above by Slim, this is a scam; the IRS always contacts by snail mail first.