BRUSSELS (Reuters) - An EU plan to begin restoring airport slot competition next year drew criticism on Wednesday from major airlines, who warned that it could lead to a return of empty “ghost flights”. The suspension of rules governing takeoff and landing rights at once-busy airports, introduced early in the COVID-19 pandemic, has become more divisive. Low-cost airlines are impatient to see a return to normal rules requiring incumbents to use 80% of their slots or cede some to rivals. The European Commission proposal would restore the “use-it-or-lose-it” rule for the northern summer season starting in March 2021, but with a lower 40% threshold. Transport Commissioner Adina Valean said the plan announced on Wednesday would “strike a balance” between fair competition and relief for airlines hit by the travel slump. “The effect of the current waiver is to freeze competition at 2019 levels without there being any requirement that capacity is actually used efficiently,” according to the proposal, first reported by Reuters. “It is time to establish a pathway to return to a normal application of the ‘use-it-or-lose-it’ rule.” But aviation industry groups led by airlines body IATA said the EU plan “does not sufficiently address the extent of the continuing crisis in air transport”, and appealed to European governments and parliamentarians to intervene. Unless amended, it “could lead to airlines being forced to operate ‘ghost flights’,” they said in a statement. Before the waiver, some carriers ran empty flights to avoid losing slots, sparking outrage among environmentalists and the wider public. IATA and airports group ACI had proposed a regime allowing airlines to return surplus slots temporarily and use only 50% of those they held onto, without losing rights the following year.