Politicians in northern England are demanding that passengers still having to use the heavily-criticised Pacer trains should be offered reduced fares.
Greater Manchester Mayor Andy Burnham, Sheffield City Region Mayor Dan Jarvis and Leeds City Council leader Judith Blake have told operator Northern that using the ageing units is unacceptable.
Northern will meet with them to discuss "what offer we can put to customers".
Pacers are 1980s-built rail-buses meant as a short-term alternative to trains.
Northern had planned to withdraw them all by the end of this year.
Managing director David Brown said it was "very frustrating" that a small number would have to be retained into 2020 as a result of delays in the construction and delivery of new trains from manufacturer CAF.
The much-derided Pacers were originally constructed from the body of a bus and were intended to have a maximum lifespan of 20 years.
They were a joint venture between British Rail and Leyland Motors.
In a letter to Northern, Mr Burnham, Mr Jarvis and Ms Blake said it was "unacceptable" that Northern would still be using Pacers into 2020, and called for an urgent meeting.
"However, the alternative of withdrawing the Pacers without any alternative replacements would be an even worse outcome," they said.
"As we are forced into accepting the temporary retention of Pacers, we expect you to commit, as a matter of urgency, to appropriate financial compensation to the passengers affected."
They said fares should be reduced on all affected routes while the trains were being used.
Commuters complained of the trains being hot, noisy and bumpy.
Student Rimsha Sawant from Blackburn said she sighs when she sees her train is a Pacer.
"They need replacing because they are not good enough," she said.
"With all the technology we have we should at least have decent trains."
Commuter Sam Brown said in the summer the heat gets trapped inside "leaving you a sweaty mess".
"It's always a massive disappointment when you see a Pacer train waiting at the platform to take you.
"They are incredibly loud when revving up, making it impossible to have a conversation with friends, and you also feel the full force of any bumps on the track," she said.
However, Sally Carter said she preferred them to more modern trains because of the seating arrangement and large windows.
"I'm rather fond of them and will be sad to see them go," she said.
Pacer trains have been regularly used on busy commuter routes, including those into Manchester, Leeds, Middlesbrough, Sheffield and York, as well as on the Merseyrail network.
As of October 2018, almost one in four vehicles operated by Northern was a Pacer, according to the Department for Transport (DfT).
A report from DfT said of the 875 vehicles in its fleet at that time, 158 were Class 142 Pacers, built between 1985 and 1987, while a further 56 were Class 144, built between 1986 and 1988.
By Danny Savage, BBC North of England correspondent
Pacers are the laughing stock, rolling stock of the north. Introduced in the 1980s, they are rail-buses originally meant as a short-term solution to a shortage of trains.
Supporters say they've helped keep certain routes open and used. Detractors say they highlight the North/South divide and are relics.
Northern promised to withdraw Pacers by the end of this year. In February, the BBC reported concerns they were unlikely to meet that target but Northern strongly denied that was the case.
They insisted they would be gone by the beginning of 2020. More recently, they have admitted some Pacer units will still be in operation into next year.
Managing director Mr Brown added: "Everyone wants to see Pacers go from the north of England.
"Nobody in Northern wants to retain the Pacers but it's something we've been forced into doing because our new trains, which are fantastic, are arriving slightly slower than we'd expect.
"It's a small number of trains for a small number of weeks on a small number of routes. We've taken the decision that this is far better than cancelling trains or running them without enough seats.
"We want to talk through how we're going to deal with the retention of those trains and what can we do for customers that will be forced to use them into the new year.
"Of course we're not ruling anything out in terms of what package we can put together for customers."
There were calls for Northern to be stripped of its franchise when "carnage" followed the introduction of new timetables in May 2018.
Its franchises cover the North West, Yorkshire, parts of Derbyshire, and the North East.