I had asked Proz support if they consider clauses like the one below (slightly edited) to be in violation of Blue Board rule number 8.
The supplier shall not publish or divulge the existence of any relationship with Acme Translation Corporation Unlimited* without the prior written consent of Acme Translation Corporation Unlimited*, which consent may be withheld at the sole discretion of Acme Translation Corporation Unlimited*.
Here is the reply (with identifying information removed):
Please note that due to the reason that similar clause is not uncommon nowadays it is not necessary to be in violation of the rule #8, unless you have been directly forced by the company to take some actions related with your LWA entry. In such case, you may report this and ProZ.com Staff will have this checked.
However, as a service provider would have to agree to the contract before working with the company and such clause may restrict service providers' ability to provide negative feedback the following note has been added to a Blue Board record “{outsourcer name}”:
“Please note that this company may require its service providers to agree to a non-disparagement clause in its terms and conditions.”
This would allow Blue Board visitors evaluating the company before working with them to take that into account.
Therefore, you may report such cases to have Blue Board visitors informed.
The note is quite discreet. One has to click on the link shown below. As far as I remember, such notes were more prominently displayed in the old Blue Board.
*) Fictional name.