I've been checking. This is absolutely not the IRS. Their contact preference is via their website. They also have local numbers they can refer you to. I live in California and this bogus number is in Washington. The IRS website verified that they would send any legal notifications via the mail.
They also had a link to report any scams, so they have a record of this phone number now.
Same story - The lady ID herself as "officer ____" and said I was being sued by the IRS and based on an audit from 08-13 that I owed the IRS $6,582 in back taxes and interest and if I did not pay, I would be arrested within 2 hours. They had my name and address but I did not ask about my SS#.
"This call is to inform you that the IRS is filing a law suit against you. Call 425-296-1450 for more information." It was a recording. I did not call the number as the IRS does not make contact by phone.