Actually lowering a salary is incredibly rare, if not unprecedented, in engineering. However, giving a zero percent raise - along with clearly explaining why -

Actually lowering a salary is incredibly rare, if not unprecedented, in engineering. However, giving a zero percent raise - along with clearly explaining why - is a clear signal that performance improvement is needed. If a salary is lowered, that would likely translate to the employee being on the brink of being fired, with large performance changes required for them to keep their job.