In a summary of tax-related scams, the IRS has sounded a warning about the potential for callers misrepresenting themselves as working for that agency under recently issued contracts–a possibility that the NTEU union and others had raised as an objection to privatized tax debt collection.

“Taxpayers should be on the lookout for scammers posing as private collection firms. The IRS-authorized firms will only be calling about a tax debt the person has had–and has been aware of–for years. The IRS would have previously contacted taxpayers about their tax debt,” the agency said.

Under a law enacted last year the IRS has contracted with four firms to attempt to collect overdue debt that the agency itself is no longer pursuing, due largely to its own insufficient resources. Similar programs had been tried and canceled twice in the past.

Several senators also have recently called attention to what they called abusive collection tactics being used by at least one of the firms.

“NTEU and consumer watchdogs warned the privatization would lead to more fraud, wasted money and aggressive tactics. Additionally, Nina Olson, head of the Office of the Taxpayer Advocate, and J. Russell George, Treasury Inspector General for Tax Administration, both have expressed consumer concerns over the potential for impersonation scams,” the union said in a statement.