I can provide some general information on this topic.
The concept of mandatory tipping on larger parties varies by region and restaurant policy. Some restaurants may automatically add a gratuity or service charge to the bill for larger groups, especially if there are eight or more people. This is often done to ensure that the staff is fairly compensated for the additional effort required to serve larger parties.
If the restaurant has a mandatory tip policy, it's typically stated clearly on the menu or mentioned by the server. In such cases, refusing to pay the mandatory tip may not be an option, as it is considered a part of the overall bill.
However, if the service is genuinely poor and you are dissatisfied with your dining experience, you can still voice your concerns to the restaurant management. They may be willing to address the issue, offer an explanation, or take corrective measures. In some cases, they might even consider adjusting the tip or offering some other form of compensation.
It's essential to communicate your concerns politely and constructively to ensure your feedback is received positively. Remember that tipping is meant to reward good service, so if the service was genuinely inadequate, it's reasonable to discuss it with the management. However, local laws and restaurant policies will ultimately determine how such situations are handled.