Refusing a pay offer on the grounds that targets must be met to ensure the extra money is basically asking for rewards without the hard work.
Being paid more than normal for work that is less than satisfactory makes no sense. Conditions such as having to meet customer satisfaction targets will work to keep rail staff delivering to the best of their ability.
Additionally, the RMT claims that it is unfair not to reward staff who are sick or on leave during the Games. But why should they get paid for work they are not doing? This is a temporary pay offer for the Olympics, recognising the challenge it will present.