Let me preface this by saying that I do not think steroids should even be controlled (require Rx, illegal to sell or trade without license, etc).
However, because steroids currently are controlled, it is possible that their source for steroids is not exactly an otherwise clean kind of person, and it is this association with their dealer which could be of legitimate concern to the NNSA/BWXT. But I very much doubt this was the concern.
Most likely, as someone else pointed out, there was a desire to terminate their positions for reasons unrelated, but a justification subject to the terms of the union agreement was needed.
Also, standard drug tests by the DoE and DoD do not look for (or at least do not record) steroid presence - the test needs to be specifically requested (for the DoD, though tests can be performed as a result of direct command, either probable cause or consent is required for the results to be applicable for Article 15, Article 1128a, and such - obviously none of this is applicable for civilian employment under BWXT).
Not BWXT, probably Wackenhut. OOps.