I'm running into this same issue, with TriNet.
Their (unhelpful) response was the following:
" To comply with IRS guidance, TriNet must “reset” your Social Security wage base limit and “reset” your Social Security withholdings whenever your employment changes from one TriNet client to a separate TriNet client and no IRS exemption, which is rare, applies. This means that TriNet uses a separate annual wage limit, contribution base and withholding threshold for each TriNet client that employs you in a single calendar year. TriNet withheld these additional amounts due to the guidance of Treasury Regulations Section 31.3511-1(c)(2), which requires TriNet to “reset” Social Security withholdings for employees who work for multiple TriNet clients in a single tax year. You are entitled to an IRS tax credit or refund for all Social Security taxes that we were required to withhold from you in 2021 in excess of $8,853.60. See Box 4 of your 2021 W-2 for the total amount of your Social Security withholdings by TriNet in 2021. Generally, you may recover your excess Social Security withholdings either by: 1. Filing an IRS Form 843 requesting a refund of the excess withholdings, or 2. Claiming a credit for the excess withholding amount in Line 72 of Schedule 5 of your income tax return on Form 1040. If you file your income taxes using a different form, you will need to consult with your tax advisor for guidance on how to claim your Social Security tax credit. We have seen valid Social Security credit claims and refund requests improperly rejected by the IRS as a result of their complex systems that may not be set up to recognize that you are a worksite employee of a PEO (Professional Employer Organization). If you receive such a letter from the IRS, we can provide you with an explanatory letter that you can use to support your IRS credit claim or refund request. Please email a copy of the letter to [email address removed]. "
All of which is to say, they know full well that the IRS is going to look askance at having Form 843 filed, but for whatever reason they're still not willing to do the obvious thing and correct it on their end. Weirdly, they're asking for me to go through the process of getting rejected by the IRS before they'll even provide support.
