(a) At any time after notice and opportunity to be heard, and for reasonable cause, the commission may suspend, revoke, alter, or amend any certificate issued under this article if it appears that the holder of the certificate has willfully violated or refused to observe any of the lawful and reasonable orders, rules, or regulations prescribed by the commission or any other law of this state regulating these pipeline or distribution systems, or if in the opinion of the commission the holder of the certificate is not furnishing adequate service, or if the continuance of the certificate in its original form is incompatible with the public interest.

(b) If and when the commission undertakes to revoke or modify any certificate on the ground that conditions are such as not to justify the number of certificates which have been granted within the territory involved, preference shall be given to certificates in order of the time of their issuance, so that those which have been issued later in time shall, other things being equal, be canceled rather than those issued earlier in time.