The Social Resistance Group of Kazakhstan told journalists that Natalya Azhighalieva was detained at a friend's apartment in the town of Zhanaozen.
The group -- which brings together opposition activists and politicians monitoring the situation with striking oil workers in Manghystau region -- said the apartment owner was also detained and the apartment was searched by police.
The group said some unknown individuals had been following Azhighalieva for several hours prior to her detention.
Aiman Ongarbaeva, a friend and colleague of Azhighalieva, corroborated the group's story, telling RFE/RL that Azhighalieva is currently at Zhanaozen police department.
Thousands of workers at OzenMunaiGaz oil and gas corporation in Manghystau Oblast have been on strike since May, demanding a wage increase, equal rights with foreign workers, the release of jailed union lawyer Natalya Sokolova, and the lifting of restrictions on the activities of independent labor unions in the region.
More than 410 of the workers have been fired since the strike began. Several others have been brought to trial on charges of organizing unsanctioned mass gatherings.
Sokolova was found guilty of "igniting social hatred" and jailed for six years last month.
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