As every one said, you need to check your Appointment letter for getting an clear idea of company's take on this issue. Companies ask you to work for a specified period (like one month or two) after resignation, so that they can search for your replacement and proper handover of work can be done.
In your case they may have recruited your replacement or may have some one in mind already, that's why they are in a hurry of relieving you so early.
Although I personally feel this practice is not rationale. An employer will not issue a relieving letter till the time they find a suitable replacement for an exiting employee, even if the employee is ready to pay compensation for rest of the period. But with an option in Employer's hands, they forget all the terms and conditions.
In your case they may have recruited your replacement or may have some one in mind already, that's why they are in a hurry of relieving you so early.
Although I personally feel this practice is not rationale. An employer will not issue a relieving letter till the time they find a suitable replacement for an exiting employee, even if the employee is ready to pay compensation for rest of the period. But with an option in Employer's hands, they forget all the terms and conditions.