Originally Posted by Bonehead
CO doesn't. Someone here will know which airline(s) do allow this.
"Day of Upgrades"...made me think of "Night of Living Dead" or something.
Complex adjectives need a hyphen, as in
"Day-of Upgrades".
Still obtuse enough to get me to look...
More descriptive and also grammatically correct would be: Upgrades on the day of travel (or more precisely, "Paid upgrades on the day of travel").