The only thing that I would add to Dr. Tam's remarks, is that, under clause 33(b) of the bill, if the person is accompanied and supervised by a person who holds a security clearance, work can go on. It is explicitly written into the bill. The other details of level of risk and who has to be subject to security will apply only to Levels 3 and 4. The concept of being accompanied is in the bill.
On March 5th, 2009. See this statement in context.