The power of subpoena -- broad as it is -- and the power of contempt for refusing to answer -- drastic as that is -- and even the solemnity of the oath cannot ensure truthful answers.
On the other hand, they will not give the slightest consideration to the fact that Iran is about to become a nuclear power, in contempt of its international obligations, and so is poised to become the gravest threat to international security in the past 25 years.
Or it could be a motion to punish the offender - Parliament has a theoretical power to jail people for contempt, and the building does contain a cell for this purpose.