Some employees who have worked for multiple employers in a single tax year may find that more taxes were withheld than the maximum for that tax year.

"When you have more than one job in a year, each of your employers must withhold Social Security taxes from your wages. This applies no matter what the other employers may have withheld. You may then end up with total Social Security taxes withheld that exceed the maximum. When you file your tax return the following year, you can claim a refund from the IRS for Social Security taxes withheld that exceeded the maximum amount."

Source: Social Security Administration