Londoners face having their £1 coins rejected on the capital's transport network this week.
The new 12-sided coins enter circulation on Tuesday - but some companies are yet to adapt machines to accept them.
London Overground and beleaguered rail operator Southern are among those who have not altered ticket machines to accept the new shape, the Sunday Times reported.
The coin is being bought into circulation in a bid to clamp down on fraud as it is said to be harder to replicate.
It will be lighter, thinner and wider than the current £1 coin.
The British Parking Association told the Sunday Times parking meters may not be equipped to deal with the coins until June.
And Tesco has admitted that trolleys at some of its supermarkets have not been adapted yet.
The new coins will replace the old ones entirely by October.
Shashi Verma, Chief Technology Officer at TfL, said: “We have been working since last year to upgrade our machines and all stations on the London Underground, Docklands Light Railway, London Overground and TfL Rail network will accept the new £1 coin once it is launched on 28 March.”