That would be a great question if 29 CFR 1904 was a statute but, of course, it is merely a body of regulations and gives the agency broad discretion.
Taxcontrol at #10 cites a statute that might control but a quick skim suggests, among other things, if COVID19 is not considered a "workplace illness" it may not apply.
Of course, if it does apply the R's ought to be making a big deal about a Biden agency overtly ignoring statutes.