This phone number Called me and left a message saying to call them back it's the IRS filing a lawsuit against me?

The IRS does not initiate communications
with a "cold call" to unsuspecting people.
Instead
The IRS first sends a letter, always!

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_Info" link, below, for lots of information and a reporting site.

USA_InfoUSA 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

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Please reply to this post, to let us know you read it, or have taken suitable actions to protect yourself.

If this number appears on your caller id, you are the subject of an IRS phishing scam.  The 509 number, a Spokane area code, is explained by the spoofers as an artifact of their using a Washington D.C.-based call center at IRS headquarters.  They will provide fake names and badge numbers and insist that your are being sued by the IRS for back taxes.  Take names and and numbers and give then no information.  Then file an attempted fraud report at TIGA.gov.