By law, which of the following is employers required to withhold from employee wages?

Employers are legally required to withhold payroll taxes from employee wages as mandated by federal and state laws. Payroll taxes generally include Social Security and Medicare taxes, known collectively as FICA (Federal Insurance Contributions Act), as well as federal income tax withholding. These taxes are critical for funding public services such as social security benefits, healthcare for the elderly and disabled, and various government programs.

In contrast, health insurance premiums, retirement contributions, and life insurance payments are typically considered voluntary deductions that may vary based on an employee's specific benefits choices and the employer’s offerings. While employers may choose to deduct these amounts from wages, they are not legally obligated to do so in the same way they are with payroll taxes. Therefore, the reason why payroll taxes are the correct answer lies in the legal framework that governs wage withholding, emphasizing the essential role that these taxes play in supporting government-funded programs.