Danny Kennedy committed to Belfast to Derry rail upgrade
Regional Development Minister Danny Kennedy has said he is "committed" to upgrading the Londonderry to Belfast rail line and has no plans to allow the service to close.
He said the project had been delayed because of budget cuts but would begin in 2014.
Local MPs have called for people to lobby for funding to secure the future of the line.
Safety work on the line is due to begin in January, the DRD said.
Mr Kennedy said: "Unfortunately, as a result of the budget approved in January of this year, the proposed £75m project to upgrade the Coleraine to Londonderry track in 2012 has had to be deferred until 2014," he said.
"However, £20m has been allocated to the 2014/15 year to allow the project to start at that time.
"In the meantime, my department is funding a programme of engineering work to maintain safety and keep the line operational."
Mark Durkan and Gregory Campbell said spending money on safety work rather than the £75m needed for the proposed upgrade was "unsatisfactory".
Foyle MP, Mark Durkan said they had been led to believe that the upgrade would go ahead.
"When we had the commitment given that the money would be here and would be coming, some of us questioned as to whether or not the timeline for that was really secure, that it was going to be hostage to other budget changes, but we were given assurances," he said.
"Now Translink say they have been faced with this cut, the current minister is saying this is the way it has to be.
"Of course it clearly does put the line in serious difficulty and why is that it is the Derry to Coleraine line that is always the after thought."
Some journeys between Derry and Coleraine will be replaced by buses.
The BBC has learned that the move is over concerns about safety.
The disruption will affect a third of trains using the inter-city route.
The maintenance work and the bussing of passengers is expected to begin early next year and will last for between 18 and 24 months.
While this work is going on, Translink said it had "no alternative but to reduce the frequency of train services in order to maintain safety standards".
Translink announced earlier this month that it was introducing a number of cost cost cutting measures.
The company will have less money to spend in the coming years as part of overall budget cuts.