Workers at an oil refinery have gone on a 24-hour strike over foreign staff being paid less than half that of UK employees.
About 20 specialist workers, employed by Italian company Nico Industrial Services Ltd, are carrying out the industrial action at the Esso refinery in Southampton, Hampshire.
Another 24-hour stoppage is planned for July 27.
A spokesman for Unite, the country's largest union, said that the Nico workers, mainly Bulgarians and Italians, were being paid about £48 for a 10-hour day, while the 270 other workers on the site employed by other contractors were earning about £125 a day.
British workers employed by Nico were also being paid the higher rate, he said.
He said the effect of the strike would be to slow up the site's refining process as the specialist striking workers clean out the catalyst converter tanks.
Regional officer Malcolm Bonnett said: "What we have here is a group of workers, who were transferred to Nico, being blatantly exploited by an employer paying less than half the going rate compared with the 270 other contract workers on the site, who are covered by national and regional agreements.
"This dispute is about trade union recognition so that our members working for Nico receive equality of pay and terms and conditions. This is a dispute about basic fairness in the workplace.
"We call on the Nico management to get around the table and talk about these important issues and avoid this dispute escalating.
"Unite won't stand by and see foreign workers being ripped off in such a grotesque manner. We won't countenance a race to the bottom in wages by unscrupulous bosses."