U.K. contract workers held unofficial strikes Tuesday at energy facilities to protest the use of foreign labor, echoing walkouts by hundreds of workers in February.

The strikes were held in sympathy with contractors at the South Hook liquefied natural gas terminal at Milford Haven in Wales earlier Tuesday, the GMB union said in a statement. The contractors objected to the hiring practices of industrial services company Hertel UK for an insulation project, the GMB union said.

"There is widespread anger and outrage at repeated attempts in different projects around the country to exclude local people from job opportunities on these projects," GMB General Secretary Paul Kenny said.

Hertel had sought - but was unable to secure - skilled laborers for the start of the three-month project, the Netherlands-based company said in an e-mailed statement.

"We have agreed with union officials that we will hire local skilled personnel once they are identified...We understand people's concerns and we have engaged in detailed discussions with trade union national officials and local representatives," said David Fitzsimons, managing director at Hertel.

Hertel said it complied with national labor agreements on terms and conditions for workers.

"The subcontractor involved is taking steps to resolve matters with its employees and it would be inappropriate for us to comment further at this time," a spokesman for the South Hook terminal said.

Unofficial strikes by contractors also occurred at the Dragon LNG import terminal in Milford Haven, RWE AG's (RWE.XE) Aberthaw Power Station in Wales and ConocoPhillips' (COP) 221,000 barrel a day Humber refinery in northern England. In February, hundreds of workers went on strike at U.K. refineries, power plants and other energy facilities after Total SA (TOT) awarded a construction subcontract at its 200,000 barrel a day Lindsey oil refinery in northern England to an Italy-based company Irem SpA.

Sites hit by walkouts in February included ConocoPhillips' Humber refinery, BP PLC's (BP) Kinneil gas processing facility, the Sellafield nuclear site, Chevron Corp.'s (CVX) 222,0000 barrel a day Pembroke refinery, the Dragon and South Hook liquefied natural gas terminals, Scottish and Southern Energy PLC's (SSE.LN) Fiddler's Ferry power station, Drax Group PLC's (DRX.LN) Yorkshire power station, and ScottishPower's Cockenzie and Longannet power plants. ScottishPower is the U.K. unit of Iberdrola SA (IBE.MC).

-By Lananh Nguyen; Dow Jones Newswires; (4420) 7842 9405; nicholas.heath@dowjones.com

(Angela Henshall, Nick Heath and Reza Amanat in London contributed to this report.)