Translink has spent tens of thousands of pounds for staff to use taxis.
Over the last three years, cab fares for staff travel cost the company a total of £175,000. And now an Assembly member is demanding that Translink chiefs explain their rising taxi bill.
DUP MLA Jim Wells quipped: "Translink has unveiled marketing slogans such as 'Let the Train take the Strain' and 'Avoid the Fuss - Use the Bus'. It would appear, however, that as far as its staff travel is concerned their slogan should be 'Its Fab to use a Cab'."
But Translink's head of marketing, Ciaran Rogan, said: "We have staff working on a 24/7 basis and often they are finishing when public transport isn't available."
The former vice-chair of the Assembly committee which monitors transport issues argued, however, the cash involved is effectively public money because Translink is so heavily subsidised.
"I can understand that if you have, for example, cleaners working until two or three in the morning there may be no other way to get them home than a taxi," the South Down MLA argued.
But Mr Wells said he believed the "vast bulk" of expenditure is down to drivers being moved from one station to another.
Mr Wells said his concern was sparked because year-on-year the total involved is escalating - in 2008/09 Translink spent £53,000 on taxi fares, for 2009/10 the figure increased to £56,000 and by 2010/11 the bill shot up to £70,000.
But Mr Rogan said the £50,000 to £70,000 spent over a year had to be put in the context of an overall company turnover of £180m.
"We will not use taxis where a public transport alternative is available," he said.
Translink has spent £175,000 for staff to use taxis over the last three years.
The company forked out £53,000 on taxi fares in the 2008/ 2009 year, which went up in 2009/10 to £56,000 and then in the last financial year further increased to £70,000.
But company bosses say that the huge sums involved can be justified.