Of course that can't be done. Employees don't have the option of "waiving" their contributions, otherwise employers would be "encouraging" such an action all the time. Frankly, who cares what the employer is "thinking". They don't know the law; that's why they pay us. The employer has to be told that this is just not legal. No more than trying to force an employee to pay back a loan made to the participant by the employer (not the plan) from the retirement plan distribution to that employee.