Several of the UK's main airports do not yet have permission to ease the one-piece cabin baggage restriction next month, the government has said.
The Department for Transport has said more than one piece will be allowed after 7 January, provided airports have purchased improved security scanners.
So far 19 airports have been given permission to relax the rule.
But several airports including Gatwick, Leeds Bradford and Edinburgh have yet to meet the required standards.
They have to prove they can cope with extra cabin bags without compromising security.
A spokesman for the Department of Transport said: "Some airports have coped with the changes, but some need to improve."
Passengers might feel confused about the different rules at different airports, he admitted, but said it was the industry's responsibility to inform them.
Malcolm Robertson, head of corporate communications at airport operator BAA, said he expected more BAA airports, including Gatwick, Glasgow and Edinburgh, to be approved by the government in the next few weeks.
He said: "We've invested heavily in new security capacity including technology and people to help the Government lift their one baggage rule."
BAA has recruited over 2,000 new security guards in the last 14 months, he added.
But he said that Gatwick airport failed to meet the targets because it had a shortage of technology and people.
Easyjet said it was worried that passengers could turn up at airports with the wrong amount of baggage.
The airline flies from Stansted airport, which is allowed to relax the bag restrictions but also from Luton, where the old luggage rules still apply.
Size limits on liquids and cabin baggage will still apply and airlines can place their own restrictions on the amount of hand baggage that can be taken in to their aircraft.
The dimensions of hand luggage must not exceed 56cm x 45cm x 25cm (22in x 17.7in x 9.8in approx), including wheels, handles and side pockets. This is equivalent to the size of a small roller suitcase.
The airports that already have permission to relax baggage restrictions on 7 January are: Aberdeen, Benbecula, Birmingham, Cambridge, Cardiff, Heathrow, Inverness, Islay, Kirkwall, London City, Manchester, Plymouth, Prestwick, Southampton, Southend, Stansted, Stornaway, Sumburgh and Wick.