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 XXIX

Canon XXIX.

Christians must not judaize by resting on the Sabbath, but must work on that day, rather honouring the Lord’s Day; and, if they can, resting then as Christians.  But if any shall be found to be judaizers, let them be anathema from Christ.

Notes.

Ancient Epitome of Canon XXIX.

A Christian shall not stop work on the Sabbath, but on the Lord’s Day.

Balsamon.

Here the Fathers order that no one of the faithful shall stop work on the Sabbath as do p. 149 the Jews, but that they should honour the Lord’s Day, on account of the Lord’s resurrection, and that on that day they should abstain from manual labour and go to church.  But thus abstaining from work on Sunday they do not lay down as a necessity, but they add, “if they can.”  For if through need or any other necessity any one worked on the Lord’s day this was not reckoned against him.