The National Labor Relations Board (NLRB) has ruled that companies cannot employ a "blanket" policy to bar workplace discussions of ongoing investigations without violating Section 7 of the National Labor Relations Act (NLRA).
(In a similar way, the Buffalo field office of the Equal Employment Opportunity Commission ((EEOC)) recently said basically the same thing regarding a workplace sexual harassment investigation. The full EEOC has yet to weigh in on the issue, however.)
In the case of the NLRB involving Banner Estrella Medical Center, the board said that "blanket" restrictions on internal discussions are forbidden by Section 7, but that individual cases can still be subject to confidentiality requirements if handled properly.
In practical terms, according to attorneys reviewing the Banner Estrella case, the ruling means that more record-keeping and paperwork will be required of companies wishing to get employees to observe an individual case confidentiality agreement (since blanket prohibitions are forbidden).