If EU this helps.
https://osha.europa.eu/en/legislatio...ive-2000-79-ec
That is worker's rights and employers duties.
But avoid jumping to conclusions. FTL rest days are not the same as those required above.
Normally airlines don't differentiate between the two types. And they can give you OFF-REST downroute legally as long as the 96 OFF-HOME + vacations are respected where they should be for the given calendar year.