It's the IRS, anything to do with them is "at your own risk". Just send the form to your former and see if he pays up. You can probably get this done without filing it. Besides, an audit might not be bad for you if you get re-classified as an employee. Chances are you paid a lot of extra tax as a sub than as an employee. If that is the case, then you will probably get a refund and the IRS will be looking at him to pay the tax instead. You can also go out and buy a copy of TurboTax and enter your tax information as you did as a sub but this time refer to the income as W-2 wages instead of 1099 pay. If the amount owed is less than what you paid, then you would be better off re-classified.
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