Every hotel will have different rules and regulations regarding accepting forms of guest appreciation. While tipping itself is proper etiquette and set by a standard, it may be required for a hotel employee to refuse a gift for various reasons. In that case, the employee should simply state the hotel policy regarding gifts of any nature. If the gift is something other than an industry standard tip, the refusal process is simple; hotel policies usually prohibit accepting gifts. In this case, a polite but firm refusal to receive the gift, along with restatement of hotel policy, is usually enough to dissuade the guests from insisting.
Employees should not accept gifts or money (other than normal and ordinary tips of normal value) from customers, suppliers or employees of other firms in the course of their work. (Award Hospitality, LLC)
An example of a polite refusal might be: "Thank you for your thoughtfulness. Unfortunately, hotel policy prohibits staff from accepting gifts from their guests; if our staff accepted gifts from some guests, it might affect our goal to offer every guest an equally-enjoyable stay. Again, thank you, but we cannot accept your gift."
Note the use of "we" to indicate that this refusal is hotel policy, not the personal objections of the employee. This allows the guest to feel that their kind gesture is simply against hotel policy, instead of getting frustrated that the individual employee is rejecting the gift or the gift-giver.
One link below gives an example of a hotel employee handbook, created by Award Hospitality, LLC.