My friend is not getting paid the same amount as his workmates because of my race?

My friend works in a restaurant as a waiter, everyone is the same age roughly and he is getting less pay. He didn't think of it at nothing at first as it was just �1 and he started later than everyone else and thought it would increase. But today he found out another person just started and that person is getting more pay. He questioned the manager & the assistant manager and she said that it was a mistake and wrote something down on a piece of paper. Later on when he was about to leave the piece of paper was lying on the desk and said 'Chinese people shouldn't get paid anyway' and the assistant manager wrote next to it 'that's what we agreed at the start haha' what should he do?