Uh oh--what year is the notice for? One of the most common ways for that to happen is if you filed a joint return, but listed all of the income under only one of the spouse's names, so that it looked like too much Social Security was withheld from only one person's wages. That would have given you a bigger refund than you should have received. Look at the W-2's you both received and see what they say for box 4. In 2016 if box 4 for one person shows more than $7347, or for 2017 $7886, then that would truly be excess SS withheld for the ONE person. You need to review the worksheets that are with your 1040 to see if you listed all of the income ( and the box 4 amounts) under only one of your names. If you did that, and received a bigger refund than you should have, the IRS wants some of it back. If you made this mistake in 2016 and transferred information in to 2017, better check to see if you made the same error.