Final answer:
Auditors should issue a disclaimer of opinion when there is a material client-imposed scope restriction as it prevents them from obtaining the necessary audit evidence to form an opinion on the financial statements.
Step-by-step explanation:
True, auditors should issue a disclaimer of opinion when there is a highly material client-imposed scope restriction. This is because such a restriction prevents the auditors from obtaining sufficient appropriate audit evidence about a significant portion of the financial statements. When auditors cannot obtain all the information necessary for their audit due to limitations imposed by the client, they may not be able to conclude whether the financial statements are fairly presented. In these cases, a disclaimer of opinion is appropriate to indicate that an opinion on the financial statements cannot be made.