Situation: Employer didn't withhold enough Federal taxes from an employee's paycheck throughout the year. The W-4 was used correctly by the employer, but the employer did not use the correct tax table for withholdings on a weekly employee vs. a bi-weekly employee. (Employee worked in California during the tax year and CA state law requires Consultants to be paid weekly which he was.)
Former Consultant filed his taxes and owes a few thousand. He's threatening to sue employer for the amount of the tax liability due to the employer's oversight in the withholdings.
What's the employer's liability in a case like this?