Crane drivers belonging to the Unite trade union will resume strike action tomorrow in a dispute over pay, which is further complicated by a bitter inter-union row.

Unite claims to represent over 90% of crane drivers, though they have traditionally been represented by SIPTU.

Last week the Irish Congress of Trade Unions upheld a complaint by SIPTU that Unite had breached ICTU rules in recruiting the crane operators and had failed to consult with SIPTU about that recruitment.

It also found that SIPTU had long-established and undisputed sole negotiating rights, except for a small number of geographical areas.

The ICTU said Unite should not seek to organise or represent crane drivers or related grades, should terminate their membership and encourage them to rejoin SIPTU.

However, Unite has announced it will be holding a nationwide strike tomorrow, and that there will be pickets at a number of construction sites in Dublin from 6am.

As a result of the pickets, workers from other unions are likely to refuse to pass the picket - though while those workers will lose a day's pay, they will not be entitled to strike pay.

The pickets will be on two SISK sites, one Cairn Homes site and one Bennett site at Capital Dock and Hannover Quay in Dublin.

Unite says it will also be holding a protest at the Health and Safety Authority to highlight concerns that workers are being issued with crane operator certificates without fulfilling the relevant training and experience criteria.

The Construction Industry Federation has warned that critical projects could be under threat and construction costs could increase by up to 30% as a result of the crane stoppages.

Director General Tom Parlon said the actions have effectively shut down sites employing thousands of workers, costing hundreds of thousands of euro per day and threatening future projects.

Mr Parlon accused Unite of being willing to undermine the industry, threaten the sustainability of multi-billion euro projects and risk all construction jobs in their attempt to poach members off fellow unions.

He said the 80% pay rise between now and 2019 sought by Unite could threaten the long-term viability of the industry.

Mr Parlon also said: "If this unlawful and irresponsible action continues, it will make it impossible for our contractors to operate, tender for work and ultimately puts construction jobs at risk."

He noted that last week the Labour Court recommended a Sectoral Employment Order for the Construction industry that included a 10% pay rise for construction workers including crane drivers.

That was in addition to the 25% increase through a "greasing time" allowance for crane drivers which was negotiated recently with SIPTU.

It remains to be seen if any construction company will take legal action in a bid to restrain the industrial action.