Answer:
A. federal employees
Step-by-step explanation:
Federal employees are allowed to unionize so that they can negotiate working conditions and have a stronger standing position before the federal government when it comes to protecting their rights.
However, they are not allowed to strike because federal workers provide a service that is considered too vital to be interrupted under any circumstance. This is why people like FBI agents, or US Army marines, can unionize, but never go on strike.