It is perfectely legal: an employer may freely instruct its employees to not discuss work with *anyone* they like--including other employees, whether out on disability, on vacation, or still at work. There is no law giving employees a right to discuss their jobs or work--it is up to employer policy and instructions.And your employer is actually correct: if you are out on disability, you are *out on disability*--you are not working. There is thin line between simply chatting about work and actually working: if you were to offer suggestions, give information or instructions, etc. to a coworker, you would be working while on disability, which is a violation of the law. It is far safer to simply ban work-releated conversations with someone on disability.