[UPDATED APRIL, 2017]
That shouldn't actually be a problem. The only truly meaningful elements on a W-2 for income tax filing purposes are your employer's federal EIN (Employer's ID number), your own Social Security Number (SSN), and your actual wage data. If there was a mistake made with any of these items, then that would definitely be a reason to have to amend your tax return.
However, with respect to the issue that you describe, you don't need to amend your return just for that.
In fact, the IRS computers and your state department of revenue really won't care, as, again, they're really just looking for the EIN, SSN, and relevant wage data. The State ID is simply a bureaucratic convention for your state; they can and will still be able to easily and uniquely identify your employer by their federal EIN, even if they have to cross-reference the Federal / State ID numbers in their database. In other words, this single issue should not affect the processing of your tax return.
If there is any issue with Box 15 that prevents e-filing your return,
and it absolutely requires a value in the software, then either use your
Federal EIN, or enter a "nonsense" value such as 12345 67890 (with a
space in the middle, or not). If the TurboTax program asks you for a
state ID number in a specific format, such as needing exactly 9-digits
and ending in XYZ, then enter a value that conforms to that format . . .
such as 123456XYZ. This will enable you to bypass the issue.
Thanks for asking this question, and good luck to you!
Regards
