Londonderry could be without a working railway line when it becomes UK City of Culture in 2013.
Improvement work on the line is due to begin in 2012 and continue for the first three months of the following year.
The SDLP MP Mark Durkan has written to Regional Development Minister Conor Murphy to express concern.
However, Sinn Fein MLA Raymond McCartney defended his party colleague's investment record.
Mr Durkan said that the proposed investment was welcome but disruption should be kept to a minimum.
"There are obvious concerns if the rail network is to be closed for a year, especially if such a closure coincides with Derry becoming the UK City of Culture in January 2013.
"I note that the Minister states that Translink will review the start date and duration, once approval for this investment is obtained," he added.
Murphy 'will respond'
Raymond McCartney said the railway line between Derry and Coleraine would not have received any new investment had Conor Murphy not become Regional Development Minister.
"When he became minister, one of his first decisions was to lift the embargo on investment on the Derry to Coleraine line," he said.
"I think first of all, this has been in the planning for a number of years and I don't think that Conor Murphy or the department knew at the time that Derry would win City of Culture.
"If it can be time-scaled to ensure we have the maximum use and the best of circumstances, I have no doubt that Conor Murphy will respond."