Airbus insists it is under no obligation to offer greater accommodation on the A320neo, having secured a tentative order for the type from budget carrier EasyJet.
EasyJet has previously indicated that it would like a higher seat-count on the A320 - which is exit-limited to 180 passengers - through a two-row addition of 12 seats. It had sought the enhancement more than a decade ago when it opted, in 2002, to order up to 240 Airbus jets.
Airbus has already embarked on a programme to raise seating capacity from 220 to 236 on the larger A321, by adjusting door positions and fitting a space-saving galley.
But its executive vice-president for Europe, Asia and Pacific, Chris Buckley, says Airbus is under "no pressure" to follow with the A320.
EasyJet says its order for 100 A320neo twinjets - still subject to shareholder approval - is "predicated" on the aircraft having 180 seats.
The airline's formal circular to shareholders detailing the fleet purchase specifically refers to 180-seat aircraft.
It says the potential order, which will include exercising options and rights on 35 regular A320s as well, will reduce the proportion of smaller A319s in the fleet from 68% to 25% by 2022.
EasyJet had been weighing the A320neo against the Boeing 737 Max, which is capable of taking 189 passengers. It ruled out the Bombardier CSeries as being "too small" for its need to expand to 180-seat jets, although the airline says it will revisit the type for a possible 150-seat requirement from 2021.
Airbus executive vice-president for programmes Tom Williams says EasyJet might have "confused" observers by stating that it was looking for aircraft with 180 seats and above - phrasing designed to avoid revealing its choice.
But he adds: "We are always looking at ways to improve our cabins and offer our customers and their passengers the best."
By 2022, says EasyJet, around 36% of the fleet will comprise the re-engined A320neo. EasyJet has yet to make an engine selection but says it has agreed a "ceiling price" for the powerplants and will enter "further negotiations to improve terms for shareholders".
EasyJet chief Carolyn McCall says Airbus offered the carrier the "best deal", with more flexibility than its competition, and with a greater discount to the list price than during its "landmark" fleet agreement of 2002.