On Wednesday four people joined the 19 workers at the plant in the village of Svetlogorye, who went on hunger strike two days ago demanding 2.7 million rubles (about $120,000) back pay.
"Now, a total of 23 people have gone on hunger strike, demanding pay arrears, 16 of them are women," Margarita Usova said.
Medics are closely monitoring the health of the protesters. On Tuesday one of the workers was hospitalized with high blood pressure, while two more women, who also have health problems, refused to be admitted to a hospital.
The plant employs 300 workers, which is about half of the town's population. With workers receiving their last pay packet in February, people have been struggling to buy basic foods and medicines.
An official from the plant's owner Russkiy Volfram said wages are unlikely to be paid until August.
Prosecutors have launched a probe into the strike.
The regional governor, Sergei Darkin, is expected to arrive at the plant to meet with the protestors.
The plant producing tungsten concentrate, opened in 1985 after a vast tungsten deposit was discovered in the area. It has experienced financial difficulties since the breakup of the Soviet Union, including over fluctuating world prices for the metal used mainly in electrical appliances.
Russkiy Volfram, the plant's owner since 2003, had its assets briefly frozen last March.