It was recently made a problem at my workplace. All known social media was checked by our managers, to see if we had selected our outsourcing company, or our client as an employer. Facebook, LinkedIn, Twitter, Instagram, Snapchat, etc. - they looked for everyone everywhere they could.
It is company policy not to discuss who our clients are, even less so to claim that we are employed by them. Our contract is with the outsourcing company, not the clients. So I guess it is justified in this case.