posted by a Canadian .
There's something wrong with this sentence but I can't put my finger on it!!
The federal government has put into effect a mandate that requires all gasoline in Canada to contain 5 percent ethanol.
Maybe another "that" after "requires"?? The "...that ____ that..." bothers me though. Too many 'that's!
and if another "that" was added then "to" would change to "must", I guess?
The sentence looks fine the way you typed it the first time. You don't need another "that" in this sentence.
The only thing I'd do to the original sentence is to remove "to" before "contain."