In the Dublin parliament assembly held on October 26, Senator Brendan Ryan, a Labour Party member, urged shoppers to buy mushrooms only in supermarkets that could guarantee pickers’ pay and working conditions are in accordance with the law.

The multiples, he said, should be bluntly told: “If you can’t guarantee that the people who produce this product are treated properly, then I won’t buy it.”

The Irish industry, worth €110m (£73.6m) to the economy, employs around 2,500 migrant workers, mainly from eastern Europe.

With the sector, which exports almost 80 per cent of its output to the UK, under pressure from falling prices and increased competition, there have been persistent reports of the migrants being underpaid and forced to work long hours.

Spokesmen for the trade union claim that as most speak little or no English, they have been slow to complain. In addition, many are said to fear that if they do complain they will lose their jobs and be sent back home.

The Irish minimum wage, at €7.65 (£5.12), is among the highest in the EU, reflecting the country’s booming economy. But in parliament, Senator Ryan complained that some mushroom pickers “are getting only €5 (£3.35) an hour for a 60-hour week, seven days a week, and being paid in cash, in envelopes without pay slips”.

The real power in the industry, he said, lies with the supermarkets, which in recent years have forced down the price of mushrooms by 25 per cent.

“This means that about six major supermarket chains could, if they wished, sort out this problem by requiring suppliers to guarantee that the people working for them are treated in accordance with the law. I am asking consumers to insist on that guarantee as the price for their continued custom,” Senator Ryan said.

The senator observed that many of his fellow parliamentarians are seriously concerned about the issue of fair trade around the world, and added: “But the place to start with fair trade is at home, and a basic principle of fair trade is that people should be employed in accordance with the law.”

Gerry Walsh of Teagasc, a farm research and advisory agency, agreed with the union spokesmen that the whole industry is being blamed for the wrong doing of a few players.

“I know how hard the majority of these growers have to work to stay afloat at a time of falling prices,” he said. “This criticism, which arises from the actions of a few, does terrible damage to the industry, both here in Ireland and in the UK. It’s not the sort of image that any sector wants to project.”