The dispute dates to June 1993 when a Tate & Lyle subsidiary, AE Staley, locked out workers after negotiations over a contract dispute broke down. The plant has since been operating with different staff.
At the meeting in London, David Watts, president of the locked-out Staley workers, said he had come "in protest at the highly orchestrated, union-busting tactics" of the company.
A Roman Catholic priest also flew in from Illinois to present a petition signed by 400 religious leaders, calling for Tate & Lyle to "live up to its responsibilities in the wider community".
A representative of the American Food and Allied Workers Union said his union would continue to try to hurt Tate & Lyle's profits to force the company to introduce a fair negotiating posture for its workers. Last October, Miller Brewing said it would no longer purchase corn-based ingredients from Staley. Unions are lobbying consumers in the US to pressure PepsiCo and Coca-Cola into finding alternative sources.
Sir Neil Shaw, chairman of Tate & Lyle, said the company was prepared to work "night and day" to find a solution. It was not a union-busting company, he said. However, he was not prepared to intervene personally.
After several questions, British shareholders complained that too much time was being devoted to the union issue and Sir Neil ruled that the meeting should move on.
Commenting afterwards, Tate & Lyle's finance director, Paul Lewis, said: "We would dearly love to end this dispute. It's not in our interests or the union's interests, but we are dealing with a minority of a minority here. It is only a fraction of the AEStaley workforce."
He said Decatur was a heavily unionised area where disputes involving other companies such as Caterpillar were also current. Since the dispute, the plant in Illinois had been operating at record levels and with a better safety record than ever.
The disruption overshadowed a statement on Tate & Lyle's current trading. Sales in the first quarter were up 10 per cent and profit was showing good progress. Analysts at brokers BZW have left their year-end forecasts of £291m unchanged.