The US company has failed to implement "fundamental changes" that would help to improve the lives of Ethiopian coffee growers, according to the directors of a new fair trade documentary, Black Gold.

Film makers Mark and Nick Francis were in Dublin last weekend for the premiere of their documentary at the Irish Film Institute.

They said it was "unacceptable" that global coffee giants such as Starbucks were making huge profits on coffee sales while coffee growers live in extreme poverty.

"We would like Starbucks and other major coffee companies to be more transparent about their business practices, " Nick Francis told the Sunday Tribune.

"All we want to know is how much they are paying their coffee suppliers. Yet even after meeting at the Starbucks global headquarters, during which we put a series of questions to the company, we have been given no answers and no indication that anything will change, " he said.

Black Gold, which will go on general release in Irish cinemas in the coming weeks, follows the struggle of an Ethiopian coffee farmer who travels around the world looking for fair price for the 70,000 farmers whom he represents.

The film focuses on the huge financial gulf between growers and sellers, with the average grower making only three cent for every 3 cup of coffee sold.

"This is the responsibility of all the major coffee companies, like Nestle, Procter & Gamble, and Kraft, " said Nick Francis. "But because Starbucks is such a recognisable high-street brand, there is an extra responsibility on the company to take the lead in changing the status quo."

The Sunday Tribune was unable to contact anyone from Starbucks for comment this weekend.