MUMBAI – A strike by some unionized workers at General Motors India’s Halol plant in Vadodara is in its fifth day, with a reported production loss so far of about 550 vehicles.

The factory builds 190 cars daily with two shifts but has been operating on a single general shift since Wednesday, when disgruntled workers on the second shift walked out.

Some 450 striking workers returned to their posts today, and the auto maker says it may be forced to take action against remaining absent employees.

The company claims inter-union rivalry is at the core of the agitation, with two unions each pressing for their own demands.

GM India signed a 3-year agreement in December with its GM Employees Union in the presence of the government labor adviser that covered “salary increases and productivity matters,” after workers struck for higher wages in October.

The most recent strike was called by a newly registered group, called the Gujarat Kamdar Mandal union, whose membership encompasses many industries and is affiliated with the political Indian National Trade Union Congress.

Gujarat Kamdar Mandal is challenging GM India’s labor agreement in federal court.

The union claims GM’s December agreement arbitrarily increased workloads 30%, created health hazards and violated three laws – the Provident Fund Act, Gratuity Norms and Industrial Safety and Health provisions.

Mihir Desai, Gujarat Kamdar Mandal general secretary, says “workers are treated inhumanly, and the excessive workload has created back pain and spinal problems for many workers.” Additionally, three workers have been suspended and some have been transferred from the manufacturing plant to dealers, “where they are required to wash the service cars.”

At GM’s insistence, the government has declared the plant strike illegal. But the INTUC says it has not received the order.

Says GM India Vice President P Balendran: “The protesting workers are continuously threatening and attempting to stop those willing to work. They spread an atmosphere of fear among their own colleagues and their behavior is improper and unreasonable. “We follow all the employment terms,” he adds. “Allegations of bias in transfers or harassment on the shop floor are not correct.”

A GM India spokesman says workers who were complaining of back pain or spinal problems have been assigned to lighter work at dealers’ service outlets without affecting their salaries. That meets their needs, he says, and should not be cause for dissatisfaction.

But there appears to be no sign of mutual understanding between the union and management, as Gujarat Kamder Mandal awaits the outcome of its court complaint.

GM last year said it planned to invest more than $200 million to modify the Halol facility to make it compatible for commercial-vehicle production in next 18 months as part of joint venture with China’s SAIC. Production will be launched in 2012.