Polling stations across Glasgow are facing disruption on election day as core members of staff plan a day of industrial action.

Several dozen janitors, who are required to be in polling stations from opening until closure, have told their employers they will only work core hours on May 7 in a row over bonus pay.

All are members of Unison and have recently joined from the GMB union. Their decision will put pressure on former colleagues to follow suit, creating a potential major headache for the city's returning officer.

The row stems from the scrapping of £40 bonus payments to janitors for working election days back in 2010.

The money was given for the additional hours worked, from opening polling stations at around 6am to closing them once the boxes have been collected after 10pm.

Janitors are also usually the designated fire warden required to be on the premises when voting is taking place, also providing security so noone intrudes into other areas of the school.

However, the cash was axed once janitors moved from being employed directly by Glasgow City Council to its arms-length company Cordia.

Unison's Alex Gordon said: "Other employees in the council family receive additional payments for the extra worked on election days. The guys from City Building receive £250 for dropping off and collecting the ballot boxes.

"Other polling station staff take annual leave and are then paid for the day. The returning officer is paid £2500 or so per constituency in the city and there seven within its boundaries.

"The jannies plan to work their normal shifts. Nothing more. It does not require a ballot. It will cause disruption, require trained fire wardens early in the morning and after 5pm and someone to open and shut the place.

"They want to send out the message to colleagues in other unions that this is their plan and hope they follow suit."

Mr Gordon said there had not been any disruption in the three subsequent elections since 2010 as the matter was only being pursued since the janitors joined Unison.

Cordia said janitors were paid for all voluntary additional hours they worked on election days. A spokesman added: "There has been no extra payment given to janitors for any election held since Cordia was formed in 2009. 

"Our formation coincided with the Council's Workforce Pay and Benefits Review, and there is no justification under that review for this payment. There will be Cordia staff present and carrying out their duties at all Glasgow polling stations on May 7."