The First ScotRail employees had been part of a group travelling back to Glasgow from a day out in the Inverness area when the alleged abuse took place.
The allegations surrounding the five employees, who are all based in the Glasgow area, date back to shortly before the start of the Commonwealth Games in July, although it is understood the group have only been suspended in recent days.
It is also understood video footage of the incident exists although ScotRail sources have denied claims the male victim was also subjected to racial and sectarian abuse.
ScotRail sources said the group had been on a golf outing during which alcohol had been consumed.
A source also claimed the firm did not immediately suspend the five, understood to have been part of a larger group, when the incident first came to light.
The source said this was because the company had been attempting to avert strike action over pay during the Commonwealth Games.
Insiders suggested that the suspensions could have exacerbated the fraught negotiations with unions so the action against the five employees was delayed until the pay talks were resolved.
One ScotRail insider said: "These five were part of a larger crowd who'd been on a golf day in Inverness. Most are drivers.
"Our understanding is one of his friends filmed it and then contacted customer services.
"There's every chance it'll turn up on a public forum. I hope now it's out there then people do come forward. Rail workers take enough abuse without our own people making it worse."
He added: "During the Commonwealth Games, management had agreed with the unions that any disciplinary action during the Games would cause problems.
"There were also concerns about adverse publicity during the Games so they put things on hold."
One source close to the case said: "There's no way any of us would condone homophobia but we'd really want to see the evidence that this has happened.
"The allegations date back to July but have only come out now due to the Commonwealth Games.
"Any disciplinary action wouldn't have been dealt with during the Games.
"If people think it was kept under wraps so pay negotiations wouldn't be disrupted that's just conspiratorial," the source went on to say.
A ScotRail spokeswoman said: "As inquiries are under way, it would be inappropriate to comment further."