Staff at gold bullion and precious metals company Johnson Matthey are on strike in a dispute over pay.
The gold bullion workers want a 4% pay rise
Members of the Iron and Steel Trades Confederation working at the company's European headquarters in
Royston, Hertfordshire, walked out at 0700 BST on Monday.
The strike at the plant, where the union has 275 members, is the first in a series of planned one-day stoppages in protest at a 2% pay offer.
The union, which wants a 4% rise, complained that executives at the company had been given pay increases of up to 22%.
The union's divisional officer Joe Mann said ISTC members at Johnson Matthey did not want to be out on strike.
He said: "However, they feel that they have no option but to take strike action in support of their claim for a 4% pay increase."
"This is less than the 6% increase
in operating profit they helped Johnson Matthey to enjoy in the last financial
year and the same as the increase in dividend for the shareholders."
More than 200 union members at the company's plant in Enfield, north London, are also due to strike next Monday.
A spokesman for Johnson Matthey said: "Negotiations continue and we hope we
can resolve this amicably."
Company sources said the pay offer was worth 3.25%.
Johnson Matthey has operations in 34 countries and employs around 8,000 people.