Elizabeth line overcharging solution sought by Transport for London
Transport for London (TfL) is working on an "urgent solution" to stop Thameslink passengers being overcharged at Farringdon station when connecting to use the new Elizabeth line.
Passengers have complained they are having to leave Farringdon and touch in on re-entry to get the correct fare.
Some have been charged the maximum Zone 6 fare when changing without touching in.
TfL has said it is going to install readers.
The new Elizabeth line opened on Tuesday with a core section running from Abbey Wood in south-east London to Paddington.
Thameslink's network runs between Bedford and Brighton via central London, including stations such as Farringdon.
It is marked on the London Underground map as a pink and white segmented line while the Elizabeth Line is marked on the iconic map with a purple and white segmented line.
A spokesman said a potential issues have been identified where "a small number of customers" changing onto the Elizabeth Line from Thameslink services.
He explained the problem originates from passengers outside the pay-as-you-go area who may have been charged a maximum fare as they have not touched in at Farringdon.
"We always want customers to pay the correct fare," the spokesman said.
"While we are urgently working on finding a more permanent solution we are encouraging customers to touch in at the ticket line or at validators on the London Underground platforms."
TfL says additional signage and TfL ambassadors are in place at Farringdon to help advise affected customers.
"Passengers who are not able to touch in can amend their journey on the TfL website or contact our customer services team to ensure they have only paid the correct fare," TfL said.
Follow BBC London on Facebook, Twitter and Instagram. Send your story ideas to [email protected]