Can a company that conducts an internal investigation tell the employees it’s interviewing not to talk about the matter while the inquiry is pending?

Not necessarily, according to a new decision by the National Labor Relations Board. The ruling applies to all businesses, regardless of whether they have a union.

Companies can insist on confidentiality only if certain conditions are met, the Board said.

The case involved an investigation by an Arizona medical center into how surgical instruments were being cleaned after a water main broke.

The medical center had a blanket policy in which it told interviewees not to discuss a matter while an investigation was going on. It explained that “when people are talking, it is difficult to do a fair investigation and separate facts from rumors.”

But the Board said this blanket policy violated employees’ legal right to communicate with each other about workplace issues.

According to the Board, a company can insist on confidentiality only if it is truly necessary to prevent a cover-up (including witnesses agreeing to lie or destroying evidence), or to stop a witness from being harmed. Further, the company must show that without confidentiality, these things are likely to happen, not just possible.

The Board said it didn’t matter in this case that the company merely requested confidentiality and didn’t actually threaten any discipline for talking – even just making the request was unlawful.

A company could presumably use other techniques short of requesting confidentiality, such as interviewing employees simultaneously to prevent them from coordinating their stories or sequestering some employees while others are being interviewed. The Board didn’t address these other approaches.