Hollywood's Martin Sheen is backing a campaign by migrant workers against alleged exploitation by the Irish mushroom industry.

He has put his name to a report detailing the alleged abuses, which include exposure to dangerous chemicals, gross underpayment and threats of dismissal if complaints are made. Sheen blames "unscrupulous employers, who exploit migrant workers' vulnerability and isolation".

He backs demands for more stringent industry control and labour inspections. Claims that workers are required to use banned chemicals such as formaldehyde are being investigated by the Irish Health and Safety Authority.

The €130m industry acknowledges there has been instances of worker mistreatment but denies the problem is widespread. Talks are underway between unions and employers to establish an effective regulatory regime for the sector.