[chipsa]

> altering her Social Security/Medicare FICA deductions in order to increase her biweekly take-home pay by a few hundred dollars.

There are no employee-end deductions you can change here. The W-4 only allows income tax deduction, not SS/Medicare. But the responsibility for ensuring it's done is on the employer, and they're responsible for ensuring the right amount, to a certain level of fidelity is withheld. And the amount she changed the total withholding is likely not enough to have triggered any IRS look into the details, and therefore criminal charges. Your restaurant owner likely was doing games enough to materially change the value withheld, which gets the IRS interested.