In a small unit, sometimes a newer nurse SHOULD float out of turn in order to keep a skilled nurse in the unit.
However, in a larger unit this should not be an issue.
And, a policy that the newer nurses ALWAYS float first is bullying.
Fortunately, I work in a closed unit - no floating.
When I DID work in a unit that floated the policy was that EVERYBODY took turns floating and the issue of experienced vs. inexperienced ONLY came up when it seriously affected the skill mix. And, that decision was made by the NM or the house supervisor at the time. The rule was, unless otherwise specifically stipulated at the start of shift, floating would occur by rotation. And even then, during times when it is necessary for the inexperienced nurses to float more, that puts the experienced nurses AT THE TOP of the list - so as soon as circumstances dictate, they float first.
Also, if this is at issue, some consideration for how it affects floating should be looked at in scheduling.
A manager that allows older nurses to bully on the newer nurses by making them do all the 'scut' work - you have to wonder how else that unit bullies its younger nurses.
Fair is fair. I think your manager has an obligation to stay on top of this issue and not let it get out of control. Issues like this create the friction that leads to turnover. Or rather, if issues like this are arbitrated unfairly, it is a sign that the manager is incapable or unable to control the power games that happen anywhere they aren't contained. Allowing those games to flourish is a failure of management.