I completely agree with you.
When I asked for a legal opinion, I did not limit the question to political activity. I asked a number of questions, and a rule preventing someone from working subsequently does indeed have legal implications relating to the Canadian Charter of Rights and Freedoms. What is most problematic is not restricting the right to political activity but rather limiting freedom of expression by preventing a person from communicating with you.
All I can say is that our rule was intended to restrict rights as little as possible in very specific situations. This would probably justifiable since we are trying to prevent any relationship with a sense of obligation. The objective of the rule justifies the restriction of rights and freedoms, which is nonetheless very clearly defined.