The ordnance factory had issued an advertisement for the recruitment of 250 labourers, CBI sources said.
However, the CBI conducted raids last night after it received complaints of irregularities in the recruitment process. An FIR had been registered in this connection on Saturday.
The raid was conducted at the exam centre and answer sheets of the written examination were recovered from the spot, they said.
A top official of the factory, leader of a trade union in the ordnance factory and an employee have come under the CBI scanner, sources added.