Helping my mother in law with her taxes and noticed her employer had different gross wages for social security/Medicare on her w2. She is an aide to an elderly woman and they do not take out any pretax deductions. The bookkeeping firm that processes them is saying they are "charging back the social security and Medicare withholdings" to her which is reflected in box 1. I have never heard of this before (owned a company so know how corporate/employee taxes work). Is this something an employer can do?

As an example, say she earned $10,000 and they report $620 as SSI withheld and $145 For mc withheld. However, they are reporting gross wages as $10765.