Brendan Howlin (Wexford, Labour) | Oireachtas source

It is a legal imperative and the indication is that a witness before a committee may be required by the committee to give his or her evidence under oath. I presume there is a sanction for somebody who obstructs the process. Part of this would arise from a determination on the quality of evidence, legal representation and costs etc., as well as anything regarded as an obstruction of the work of the committee.