There is a widespread IRS (or CRA) or "tax scam" being practiced by scammers on both USA and Canadian residents.
USA tax payers, click on the "USA Information" button, below, for lots of information and a reporting site.
USA tax payers should read this:
http://www.irs.gov/uac/Newsroom/Phone-Scams-C ... 5-Filing-Season
Short answer:
The IRS never initiates a contact via phone.
They always send a snailmail first.
If you were contacted by an IRS impostor, you may file a report, after clicking on this link:
http://www.treasury.gov/tigta/contact_report_scam.shtml
Recent news story:
http://www.wltx.com/story/money/2015/03/12/fa ... -scam/70202814/
Congressional hearing:
http://www.nbcnews.com/business/taxes/tax-imp ... hearing-n341906
Canadian tax payers should read this:
http://www.cra-arc.gc.ca/nwsrm/lrts/2013/l131210-eng.html
This scam is also described as scam #11, here:
http://phonehelp.2truth.com/facts.html