Striking Vodacom employees were outraged that the company had blocked their cellphones, the Communication Workers Union (CWU) said on Friday.
This came after the service provider blocked the strikers' cellphones, citing a "no work, no pay, and no benefits" policy.
CWU spokesman Mfanafuthi Sithebe said: "Vodacom confirms our long-held view that the company has employed reactionary expatriates with no knowledge of the labour laws and the supreme law of the country."
He hoped Vodacom would not extend its "no benefits" policy and cut off medical aid too.
Vodacom spokesman Dot Field said on Thursday that strikers had been locked out.
Field said the actual cellphones were not blocked and the workers were free to insert their own SIM cards into the handsets.
Sithebe said: "The shallow legal opinions by Vodacom legal services is nothing else but tactics aimed at undermining endeavours by the department of communication to normalise the situation." - Sapa