The restrictions, the highest possible, mean non-essential shops must close from 24 December and holiday accommodation will shut from 28 December.
The lockdown has no end date and will only be reviewed every three weeks.
The order was given by Welsh first minister Mark Drakeford amid concerns about spiralling Covid rates.
The Welsh government said on Wednesday that guidance published by Drakeford would be formally set out in regulations.
TTG is seeking clarity from the Welsh government on what constitutes "non-essential retail".
During the latest lockdown in England the UK government confirmed it was not closing travel agents by law, "as these businesses can continue to operate remotely and it may be necessary for people to continue to go to their office where they cannot work from home".
