Union concerns over Rotherham and Sandwich construction worker pay
Construction workers building two biomass plants are being underpaid, according to the unions Unite and GMB.
Officials said pay for sub-contractors working in Rotherham and Sandwich was up to 61% below the agreed rate.
Union representatives have travelled to Copenhagen to protest outside the offices of Pension Danmark, which is financing the projects.
Pension Danmark said it was in talks with the unions and "did not support undercutting rates".
Phil Whitehurst, national officer of the GMB, said: "This exploitation of workers and social dumping has got to stop and if it takes civil disobedience on the gates of their construction projects in the UK, so be it."
Work on the Templeborough Biomass Power Plant, in Rotherham, is being undertaken by Babcock & Wilcox Vølund (BWV), which is said to be sub-contracting the work to Croatian company Duro Dakovic.
Work at the plant in Sandwich, in Kent, is being overseen by Burmeister & Wain Scandinavian Contractor (BWSC).
The unions say both firms are ignoring the pay levels stipulated in the National Agreement for the Engineering Construction Industry.
Following a meeting with GMB and Unite representatives, Pension Danmark's senior vice-president Jens-Christian Stougaard said: "Some of the points have been put forward before and there has been an ongoing dialogue between the parties involved.
"When we invest - being directly or through Copenhagen Infrastructure Partners (CIP) - we have, among other things, clauses regarding wage and work conditions which also apply to subcontractors.
"Of course we do not support undercutting rates."
BWV said "everyone has a right to fair and reasonable employment and conditions, and that our workers and those of our subcontractors are provided with fair pay and safe working conditions comparable to similar projects in the UK and in accordance with the law".
Christina Sorensen, senior partner at CIP, said its contractors had an obligation to "pay rates of wages, and observe conditions of labour which are not lower than those established for the market where it is carried out".
She said both BWV and BWSC had adhered to the contract "to our satisfaction" and if they did not CIP would ask them "to correct" any issues.
The BBC has contacted BWSC for a comment.