Can the Government mandate exclusivity among subs?

A presolicitation document issued by a federal agency contains the below question and answer, which appears to me as Government-directed exclusivity. This creates the concern among companies interested in participating as subcontractors that they must choose the single best team to join, as opposed to participating on multiple teams. Is Government-directed exclusivity allowable? Does anyone have an alternative read on this?

Question:

Would it present any issues if a company was included on more than one response?

Answer:

It would not be an issue responding to the sources sought to be included on more than one response,

however, during the competition phase it would be an issue. Your company would need to select one small

business to team with during competition.

If my interpretation is accurate, such a requirement would be anticompetitive and a serious interference in commercial relationships. I've never heard of anything like this.