I remember work to rule well. As a kid my teachers union were going through negotiations and on the verge of striking and we got to see first hand what that's like. Turns out all those sports and extra curricular activities your kids enjoy in school aren't in the contract. Same with staying late and providing any extra help, or supporting anything like a school dance. The contract is just show up, lecture, mark homework during prep. periods, leave. Parents were frustrated to say the least. Anyways, you can't expect your employees to go above and beyond for free. Any extra responsibilities need to be spelled out in the contract.

I can't imaging how that'd work for a developer. There can be an innumerable number of tasks different developers do and as they grow in a position, it can change enormously. I guess it would force contract and pay renegotiations every year? Otherwise your new team lead could just.. stop.. in the case where they were hired as just a senior developer.