The Suid-Afrikaanse Onderwysers Unie (SAOU) has been ordered to pay costs after losing a court application against the Gauteng department of education.
The teachers' union took the department to court last week in an attempt to compel it to repay and stop what it calls "unlawful deductions" from its members' salaries.
The case was postponed to yesterday at the Johannesburg labour court where the application was dismissed.
In its application the SAOU claimed that its members had participated in the public service strike earlier this year for only one day, on June 1, and others did not take part at all.
However, the union stated that the salaries of thousands of its members were docked in September and October as a result of the month-long strike.
It said the deductions were unlawful and unfair.
The department's spokesman, Kate Bapela, said they were willing to listen to queries from teachers over the deductions.
"Teachers have to provide proof that they did not participate in the strike. If it emerges that some deductions were made erroneously, teachers will be reimbursed accordingly," she said.
The SAOU has succeeded in similar applications against the education departments of KwaZulu-Natal and Limpopo.