A large number of crane drivers on some of Dublin’s highest-profile building sites were simultaneously unavailable for work last week as a pay dispute in the construction sector worsened.

As many as 80 per cent of crane operators on sites in Dublin city did not show up for work last Tuesday bringing building work to a halt. The operators were struck down by what sources described as “crane flu”.

“The absent drivers seemed to have similar symptoms to the infamous Blue Flu which struck down Gardai almost two decades ago,” said a construction industry source.

Many of the highest-profile building sites in Dublin’s booming Docklands and elsewhere in the city were unable to function when the operators did not show up for work.

Crane Operators are key to the operation of major building sites and their absence brings nearly all work to a halt.

Industrial unrest in the industry comes at a time when construction output – particularly in commercial and housing – has accelerated.

That has also led to an uplift in employment, with tower cranes multiplying across the city skyline. But last Tuesday’s mass absenteeism came after many crane operators changed trade union as a pay dispute threatened to escalate, it is understood.

Many were previously members of Siptu but were forced to bargain for pay on each individual building site after a registered employment agreement for construction was struck down in 2011. They had asked the trade union to lodge a general wage claim for €27 an hour but the union had not done so, according to sources.

The crane operators then joined rival trade union Unite, which had agreed to progress the pay claim, although there is no suggestion that last Tuesday’s crane flu outbreak was orchestrated by that trade union. When contacted, Unite did not take the opportunity to respond to queries on the dispute.

Other categories of construction worker are also understood to be contemplating a similar transition to Unite, a major blow to Siptu’s construction sector.

Banksmen – workers who direct crane operators via radio from the ground – are now also in discussions about their own wage levels and union representation, according to sources.