Power to summon: compellable attendance and document production under customs law subject to supervisory authorization and safeguards. Power to summon persons under the Customs Act permits Gazetted Officers to compel attendance and production of specified documents or all documents of a described class; summoned persons must attend, state the truth and produce materials, and such inquiries are deemed judicial proceedings. Board guidelines require prior written authorization for summons by Appraisers or Superintendents (or oral permission later reduced to writing where necessary), recording of reasons and filing of a report, and caution against summoning senior management at the initial stage absent indicia of involvement.