The team has never been referred to as Justice League on screen. They have been referred to as:
■ In the episode Run, Bart mentions to Clark that the two of them and other people like themselves should "form a club or a league or something". This is a reference to the Justice League of America.
■ Emil Hamilton referred to them as "Oliver and the league" in Rabid.
■ Rick Flag when he was Oliver he called his "vigilante" team a "League of heroes" in Shield.
■ Dinah Lance calls them "The League" while talking to Clark in Collateral.
■ In the episode Justice, Oliver said that their team...