ITINs (Individual Taxpayer Identification Numbers) now can expire.
An ITIN is a tax processing number issued by the IRS to individuals who need to have a U.S. taxpayer ID number (for example, for individuals who need to file a U.S. tax return). These individuals are not eligible for a social security number.
Some of the most common reasons to have an ITIN is if the individual needs to file a U.S. tax return because they have U.S. source income (such as a U.S. rental property or the sale of U.S. real estate). It used to be that ITINs did not expire. So if an individual didn’t have to file a U.S. return every year they could continue to use the ITIN only when they needed to file a return.
A good example of this is a U.S. nonresident alien who only needed to file a U.S. tax return when they sold a U.S. property. This has now changed. ITINs which have not bee used on a federal tax return at least once in the last three years will need to be renewed.
Other ITINs (depending on the #) may also expire. This may catch some U.S. tax filers unawares. Check out https://www.irs.gov/uac/newsroom/irs-now-accepting-itin-renewal-applications-taxpayers-encouraged-to-act-soon-to-avoid-processing-delays-in-2017.