UNIONS have threatened a rail strike during the Christmas period after a ticket inspector was sacked over claims he was intimidating and aggressive towards a holidaymaker.

The National Union of Rail, Maritime and Transport Workers (RMT) is balloting members over industrial action as it steps up its campaign to reinstate Scott Lewis, of Glasgow, who was dismissed following an incident involving a passenger on a train to Prestwick Airport.

The passenger is understood to have been using a special deal that gave free travel to those flying from the airport.

However, a dispute broke out between Mr Lewis and the man over his ticket, which left the customer clearly distressed, according to industry sources.

ScotRail said the conduct of 40-year-old Mr Lewis had fallen well below what was expected of staff but unions claim the company had "not one shred of evidence" to back up claims the ticket inspector had left the passenger in a state of alarm.

Ballot papers were due to be distributed to members yesterday, with a RMT spokesman saying a walkout by ScotRail staff in the run up to Christmas could not be ruled out.

Business leaders have condemned any action over the festive period, given the potential impact on retailers and possible road congestion.

A ScotRail spokesman said it was hoped that staff would take a common-sense approach by acknowledging Mr Lewis's conduct was unacceptable.

He added: "Terminating any member of staff's contract of employment is not taken lightly or without justification. The standards of conduct fell well below what we expect.

"The facts identified by the detailed investigation are very different from those described by the union.

"There was a complete disregard to procedures for dealing with a customer, and the RMT is fully aware of that and other grounds for dismissal."

Mr Lewis had 19 years' experience of working on the railways and a number of commendations from his employers, RMT said.

It claimed Mr Lewis was dismissed for allegedly making "unwanted contact with the passenger" but ScotRail said this was not the case.

According to industry sources, Mr Lewis refused to accept the customer was allowed free travel under the special deal to promote a new route at the airport. The dispute is believed to have been captured on CCTV.

The union said their member was following company policy in the event of non-payment of a correct fare.

Mr Lewis was dismissed in July following the incident in March, with the issue also to be taken to tribunal.

RMT said it was to withdraw its support for ScotRail's policy on assaults on staff along with three other unions, claiming it weighed the procedure in favour of the passenger in the event of an allegation of a dispute with an employee.

Bob Crow, the general secretary of RMT, said: "Scott Lewis has been victimised and sacked for trying to help a passenger within the written procedures set out in ScotRail's own policies in what is an absolute travesty of justice.

"RMT will not sit back and watch while our members are picked off in this fashion by a management who think that they can fire staff without a single shred of evidence to support their case.

"We will be calling for a massive 'yes' vote for action in this ballot and would call on ScotRail to see sense and reinstate Scott Lewis."

Lauren Paterson, senior policy executive at Confederation of British Industry Scotland, described the strike threat as regrettable.