Image: PA
The government will decide "within weeks" whether to strip Govia Thameslink Railway of its franchise, the Transport Secretary has said.
Chris Grayling has been answering MP's questions about a timetable overhaul that caused chaos this summer.
He said: "We are finalising the action... It could involve penalising [or] taking the franchise away."
But he cautioned that it would have to be on a "legally sound basis" and in passengers' best interests.
GTR has been contacted for a comment.
The shake-up started on 20 May and saw every train time on each GTR operation change, affecting an estimated half a million commuters.
'Utterly unacceptable'
Passengers were warned of disruption but the implementation of the new timetable saw some services withdrawn and further cancellations made without warning.
GTR said at the time that introducing the new timetable was a "significant logistical challenge" and apologised for "any inconvenience caused" to passengers.
Mr Grayling told MPs on the Transport Select Committee there was a "systemic" problem and he wanted to see "wholesale change in this industry, we need to be much more joined up".
He insisted "it is not the government's job to run train timetables" but said "the performance failures this summer were utterly unacceptable".
Mr Grayling said: "They clearly have not met their contractual requirements. We are finalising the action we will take."
He said the decision on GTR - which runs Southern, Thameslink and Gatwick Express trains - would be made soon.
"We will make sure there is a consequence to the under-performance of GTR this summer within a small number of weeks," he said.
Mr Grayling also told the committee that London mayor Sadiq Khan's decision to freeze single fares across the Transport for London (TfL) network left the body in "deep financial difficulties".
"The problem with a fares freeze - if your costs continue to go up every year, if you're continuing to pay more to your staff - is that you build a long-term and growing underlying problem within your own finances," he said.
"The only way of counteracting that is people who don't travel on the railways have to pay more and more in taxes."
Source: BBC