From Longman Dictionary of Contemporary Englishextraordinary meeting/session etcextraordinary meeting/session etcMORE/EXTRAa meeting which takes place in addition to the usual ones → extraordinary
Examples from the Corpus
extraordinary meeting/session etc• And the Press Council called senior editors to the first extraordinary meeting convened in its twenty-seven-year history to discuss the matter.• The announcement came two hours before an extraordinary meeting of Bryant shareholders that had been expected to approve the merger with Beazer.• Already he has called an extraordinary meeting of directors and supporters to discuss his radical new proposals. 