§40.21 requires an employer to obtain a waiver to do one very specific thing: remove employees from performance of safety-sensitive functions on the basis of the report of confirmed laboratory test results that have not yet been verified by the MRO.
An employer does not need a §40.21 waiver to take other actions involving the performance of safety-sensitive functions.
For example, an employer could (if it is not prohibited by DOT agency regulations and it is consistent with applicable labor-management agreements) have a company policy saying that, on the basis of an event (e.g., the occurrence of an accident that requires a DOT post-accident test, the finding of reasonable suspicion that leads to a DOT reasonable suspicion test), the employee would immediately stop performing safety-sensitive functions. Such a policy, which is not triggered by the MRO`s receipt of a confirmed laboratory test result, would not require a §40.21 waiver.
It would not be appropriate for an employer to remove employees from performance of safety-sensitive functions pending the result of a random or follow-up test, since there is no triggering event to which the action could rationally be tied.