Former employees of mobile phone operator Dtac say they intend to petition the Labour Ministry to order the company to reinstate them, claiming they were made to resign against their will.
They say they were laid off after they succeeded in establishing a Dtac labour union late last year.
Somboon Sapsarn, adviser to the labour union, said executives demanded in January that seven employees resign in exchange for 10 months' salary.
If any of them refused they would have only received the standard severance package, Mr Somboon said.
Four more staff members met the same fate last month, he said, adding the employees were treated unfairly.
The Dtac labour union intends to file the petition for their reinstatement with the ministry this week.
Somsak Wuthphanich, one of the laid-off workers, said he had worked for the company for about 20 years and was suddenly told by his bosses he was no longer needed.
One Dtac executive denied forcing out the employees who established the union.
He said some union members were concerned about the effects of the company's corporate restructuring last year.
At the time, Dtac encouraged 10 non-performing employees to join an early-retirement package, he said.
"The company agreed the employees had the right to form a union. There was no connection between this and the company's restructuring," he said.
Darmp Sukontasap, chief of corporate affairs at Dtac, said the company views positively the establishment of labour unions within the framework of the law. Should a labour union be established accordingly, Dtac and its management team will recognise such organisations and work towards developing a dialogue with its representatives.
This means the Dtac management team will not discriminate against employees who are members of a union.
"At the same time, we expect employees and managers to act in accordance with the Dtac code of conduct and relevant laws," he said.
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Writer: Penchan Charoensuthipan & Komsan Tortermvasana