UNDER THE TABLE

Meaning: when you do something under the table – means you do something secretly, in most cases because it’s unethical or beyond the law.

For example:

Most of the salaries in Ukraine are paid under the table, because the law doesn’t leave a lot of alternative…
Many experienced English Mafia Club members know how to hold “under the table” conversations, so they don’t get penalties for breaking the rules…

You can practice this idiom soon at one of the English Mafia Club’s upcoming meetings: https://englishmafiaclub.com/events/upcoming-events