Virgin Trains has delayed the introduction of new uniforms after some female staff said blouses were see-through and too low-cut.
The UK rail operator is now offering £20 (€24) vouchers for women employees to buy undergarments to save them any embarrassment.
The problem came to light after trials of a new uniform on Virgin's line between London and Glasgow.
Virgin said it consulted widely, but it was not clear how the new uniform would be received until it was actually worn.
The Transport Salaried Staffs Association said staff had complained that the red-coloured blouses were too flimsy and would allow male passengers to see dark bras underneath.
General secretary Manuel Cortes said: "Our female members are upset because they feel Richard Branson is cutting corners by asking them to wear flimsy blouses which are skimpy and they feel too revealing.
"He asked Vivienne Westwood to design the new uniform for his air crews.
"Unfortunately, it looks like he is getting the blouses for train crews from Del Boy at Peckham Market."
A Virgin Trains spokesman said the launch of the new uniform had been delayed to allow more feedback from staff.