Airport staff last night voted to reject Dublin Airport Authority proposals which would have led to full co-operation with Ryanair's new online check-in system.
Improved work and pay conditions offered by the authority to 350 security workers were last night defeated by a majority of two to one.
Before balloting began last week, Siptu had promised to begin operating Ryanair's online check-in service from today if its members approved the authority proposals.
Authority spokesman Vincent Wall last night said the authority was extremely disappointed with the outcome of the ballot and would be seeking an urgent review through the Labour Relations Commission.
"The introduction of the electronic boarding cards makes air travel easier for passengers . . . the validation of these e-boarding cards does not impose any additional responsibility on the company's passenger screening staff," Mr Wall said. The authority had co-operated fully with Siptu in recent weeks, he added.
Last night, a union spokesman said the size of the defeat had been surprising. Some security workers would have benefited from an extra €80,000 over the duration of their careers if they had approved the improved terms and conditions, he said.
The union must now begin the process of reviewing the authority's proposals and finding a solution to workers' grievances regarding conditions of annual leave, time-in-lieu, changes to the incremental pay scale and shift rosters.
Since the official launch of the Check "N" Go service on the Dublin to Cork route last month, security staff at Dublin airport have consistently refused to co-operate with the system.
Passengers with e-boarding cards have been told by security staff to go to the usual check-in desks.
Last night, Ryanair said that talks between the authority and its employees were a matter for the authority and not the airline.