We do, and it's not a department-specific policy, but a Government of Canada communications policy.
No public servant, no matter what their classification, no matter what their level, is free to speak to the media at will or in response.... There is a communications policy in place. We have media relations officers, and journalists know this. This is really to consider who is in the correct or best position to respond. Many times it's the minister who is the appropriate person to respond. Sometimes it is a scientist. When the questions are detailed and technical on the science, that's when a scientist is in the best position to respond.