Currently, 1,800 employees working in two shifts are staging the protest", Ashok Leyland Employees Union sources said.
Speaking on condition of anonymity, they said the Union had demanded 10 per cent hike in bonus. "They rejected our request and said only five per cent was possible which we did not accept", the sources said.
They claimed that employees working in the company's other manufacturing facilities would soon join the strike.
To a query, another union official said the company had offered 5.34 per cent bonus for the 2017-18 fiscal.
"This (financial) year we want them to give us 10 per cent since the company has made profits", he said.
For 2018-19 fiscal, the Chennai-based firm reported a consolidated profit of Rs 2,194.6 crore as against Rs 1,813.82 crore in the previous year, an increase of 21 per cent.
Last year, Ashok Leyland inaugurated its cutting edge technology Electric Vehicle facility at the Ennore plant, the country's first integrated facility for design, prototyping, testing, process prototyping and solutions design.
Company officials declined to comment on the strike when asked for their reactions.