What seemed like ought to be a totally straightforward question turned out to be surprisingly disagreed on when I searched for this on Google. Some people claimed a team could receive up to 4 cards in a World Cup match and still go on playing, because the minimum number of required players on the field is seven. Others claimed that you are allowed only two, and your third red card causes you to forfeit the game entirely. Which is it?
FA Law 3
Play may not start or continue if either team has fewer than seven players, of whom one must be the goalkeeper.
If a team with only seven “loses” another player the referee is not obliged to stop the game immediately but can allow the advantage to continue until the ball goes out of play. The game cannot then be restarted.
I guess a tournament may by conducted under agreed by-laws but I can’t find any reference that FIFA does.
I don’t think the World Cup is any different. FIFA pride themselves on keeping the laws identical for whatever level you are playing at.