According to the 2016 General Instructions for Forms W-2 and W-3 published by the IRS:

• New Due Date for Forms W-2 — January 31, 2017 is now the due date for filing 2016 Forms W-2 and W-3 with the SSA, whether filing using paper forms or electronically. (Forms W-2AS, W-2CM, W-2GU, W-2VI, and W-3SS are also included.)
• Extensions Not Automatic — Extensions of time to file Form W-2 with the SSA are no longer automatic. For filings due on or after January 1, 2017, one 30-day extension may be requested. However, the IRS will only grant the extension in extraordinary circumstances or catastrophe.
• Higher Penalty Amounts — Higher penalty amounts apply to returns required to be filed after December 31, 2015 and are indexed for inflation.

More detailed information is available at https://www.irs.gov/pub/irs-pdf/iw2w3.pdf.