I do not recommend giving cheque without any date,but it depends on your conditions there.
Do you handle cash transactions/purchases/invoicing etc?
If everything is clear from your end, state the same to Management and collect the originals,leave for your higher studies.
Whatever employer is doing, it is immoral and illegal. If under pressure you are forced to give a blank cheque, make it account payee and give it. Instruct the bank to not to honour it, this is with in your right.
Please be careful in case if you have to sign any document given to you by your employer, sign it after reading and understanding it properly.
Please do not succumb to any bully or pressure.