Two possibilities.
1. If you earned more than $137,700 combined, then you paid more total social security tax than allowed, even though each employer withheld less. You will get a refund on your tax return.
2. Turbotax is very sensitive to rounding of numbers and exact percentages. If one of your W-2s is even 1 penny over exactly 6.2%, it will throw a red flag. You can get rid of this problem by changing the box 4 social security tax on the offending W-2, lower it by a few cents or take the cents off. This will not cause a problem with your tax return or with the IRS.
