MILWAUKEE (AP) -- The state Department of Revenue today is urging taxpayers to contact credit bureaus to guard against identity theft after acknowledging late last week that Social Security numbers for 171,000 taxpayers inadvertently ended up on mailing labels.

The department first notified people and post offices of the misprint on Friday night, after it heard from people who had received the mailings earlier in the day.

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Department spokeswoman Meredith Helgerson says by yesterday afternoon, some 54,500 undelivered booklets had been retrieved from post offices in Portage, Madison and Oshkosh.

This means the remainder of the mailings - now estimated at 171,000, up from 170,000 - were delivered in the past few days.

She says the department provided a file to the printer with confidential information such as names, addresses and Social Security numbers, which has been done in years past, but this time the numbers ended up on the labels.

The department said the name of the company was Ripon Community Printers and they've were paid $22,000 for the service this year.

Company president Andy Lyke says they're trying to figure out how the numbers ended up on the labels and they regret the error.