India is expelling half the staff at Pakistan's high commission (embassy) in its capital Delhi, accusing diplomats of spying and dealing with terrorists.
India will also reduce staff by the same number at its high commission in the Pakistani capital Islamabad, the external affairs ministry said.
There was no immediate response from the Pakistani authorities.
Relations between the nuclear powers were already tense after India expelled two Pakistani staffers three weeks ago.
They were accused of trying to obtain information about Indian troop movements.
Indian media suggest the latest move was prompted by the alleged mistreatment of two Indian staff members in Islamabad.