Epf over rs. 15000 limit

I have a query regarding EPF. In an establishment, if an employee's wages is Rs. 14000/- per month on which PF is being deducted regularly but in next month his salary increased to Rs. 16000/- per month. Is it compulsory to deduct the PF as wages crosses Rs. 15000/- limit? And if Yes, then on which amount PF is deducted i.e. Rs 15000/- or Rs. 16000/-.