Another possible basis for challenge arises from the limits of the federal government’s authority over interstate commerce, an area where, as in the Affordable Care Act individual mandate case, the Supreme Court’s thinking has evolved since OSHA was founded. Yet another, which might rest on a statutory or constitutional basis, could arise from the decree’s expected lack of provision for religious accommodation. Challenges on these grounds might or might not prevail. But if someone tells you that what Biden announced Thursday rests only on OSHA’s accepted and uncontroversial legal powers, they’re scrubbing away a whole lot of legal complication.

And that’s all aside from the big legal fact here: Courts have applied tougher scrutiny to OSHA’s emergency decrees than to its garden-variety rules. That is why a recently updated Congressional Research Service report on OSHA’s ETS authority as applied to COVID-19 notes that the agency “has rarely used this authority in the past—not since the courts struck down its ETS on asbestos in 1983.” (It did issue an ETS for healthcare workers and COVID-19 in June.)

As attorney Michael Schearer points out, of the nine times OSHA used its emergency power until this summer, three went unchallenged, but of the six that went to court, only one instance was fully upheld. All the others were stayed or vacated, in one instance partially. In other words, the courts have by no means been pushovers for OSHA ETSs.