Christmas Metrolink services could be thrown into chaos if drivers vote for strike action in a row over union recognition.

Around 100 staff are being balloted and if the result endorses industrial action, then 24-hour stoppages could follow.

It is believed that around 100 of Metrolink's 160 drivers are involved in the threatened industrial action. They are members of ASLEF which is demanding recognition from Metrolink bosses.

However, system operators Serco Metrolink say they inherited a single union recognition agreement with the TGWU, giving that union exclusive negotiating rights for all Metrolink staff, including drivers.

The company claim that ASLEF had earlier agreed not to seek recognition at Metrolink without the prior consent of the TGWU. This followed talks between both unions and the TUC.

But this week, Metrolink said: "That consent has not been given, nor even requested.

"Consequently, for Serco Metrolink to recognise ASLEF would put us in breach of our agreement with the TGWU and at risk of industrial action from them.

"It is the firm view of Serco, TGWU and the TUC that the proper forum for resolving this matter is under the TUC inter-union disputes procedure. ASLEF has now agreed to a request to meet the TGWU and TUC."

Commenting on the ballot, the result of which should be known on Sunday, Serco Metrolink continued: "We deeply regret the stance taken concerning the threat of disruption to Christmas services by ASLEF.

"Serco wholeheartedly embraces the union concept and has unrivalled good relations with the union movement, including ASLEF."

An ASLEF spokeswoman at their London headquarters denied the union had broken the earlier agreement and had actively sought membership among Metrolink drivers.

She added: "That is certainly not our view. We represent train drivers right across the whole country. If people choose to join ASLEF, then that is their choice. In practice, it is quite likely that drivers are going to want to join a specialist train drivers union".

She said if the ballot was in favour of industrial action, it was a requirement to give Metrolink ten days' notice.

She added it was not clear what form of action would be taken, but admitted it could involve 24-hour stoppages.