No, they cannot to this: employers may not make any deductions from paychecks (other than income tax withholding, UI, social security, etc.) without employee consent. They are free to have a policy that if you don't contribute, you can't use the coffee machine and can't even offer coffee to your customers, which probably makes $10 a month a bargain, but if you're willing to suffer that consequence, they can't force you to pay.