Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods.: Canon XX

Canon XX.

If any one shall, from a presumptuous disposition, condemn and abhor the assemblies [in honour] of the martyrs, or the services performed there, and the commemoration of them, let him be anathema.

Notes.

Ancient Epitome of Canon XX.

Whoever thinks lightly of the meetings in honour of the holy martyrs, let him be anathema.

Hefele.

Van Espen is of opinion that the Eustathians had generally rejected the common service as only fit for the less perfect, and that the martyr chapels are only mentioned here, because in old times service was usually held there.  According to this view, no especial weight need be attached to the expression.  But this canon plainly speaks of a disrespect shown by the Eustathians to the martyrs.  Compare the twelfth article of the Synodal Letter.  Fuchs thought that, as the Eustathians resembled the Aerians, who rejected the service for the dead, the same views might probably be ascribed to the Eustathians.  But, in the first place, the Aerians are to be regarded rather as opposed than related in opinion to the Eustathians, being lax in contrast to these ultra-rigorists.  p. 101 Besides which, Epiphanius only says that they rejected prayer for the salvation of the souls of the departed, but not that they did not honour the martyrs; and there is surely a great difference between a feast in honour of a saint, and a requiem for the good of a departed soul.  Why, however, the Eustathians rejected the veneration of martyrs is nowhere stated; perhaps because they considered themselves as saints, κατ᾽ ἐξοχήν, exalted above the martyrs, who were for the most part only ordinary Christians, and many of whom had lived in marriage, while according to Eustathian views no married person could be saved, or consequently could be an object of veneration.

Lastly, it must be observed that the first meaning of σύναξις, is an assembly for divine service, or the service itself; but here it seems to be taken to mean συναγωγή the place of worship, so that the συνάξεις τῶν μαρτύρων seems to be identical with martyria, and different from the λειτουργίαι held in them, of which the latter words of the canon speak.