There is one more issue in this which I didn't considered at first.
If it was merely the increase in the income without any shortage of tax then the tax department would not have sent the notice. It appears that there is default in deduction of Tax at source. TDS should have been less than the tax payable (I am qute sure of this)
I AM PRESUMING THAT SALARY WAS ACTUALLY PAID AND WAS NOT OUTSTANDING (let me know if this presumption turns out to be wrong) [Quite sure of this aswell]
This means that your employer has not complied with provision of S.192 as per which tax on salary has to be deducted at the time of payment.
Since the employer also did not deducted the tax, he too is at fault.
Ideally in such a situation , the employee is to pay the tax because as per S.15, salary is taxable on acrural basis (whether received or not) and EARLIER when employer would deduct the tax and pay it, then the employee can claim refund of the tax so paid by himself (so in net,to some extent the liability is born by the employer.
[There would be little or no interest liability, if assessee paid it timely]
Now, there have been an ammendment, as per which if the employee had paid the tax so due and showed this in HIS (employees) return filed within due date, then employer would not be treated as assessee in default and it would be deemed that he did deducted the tax and paid it.
But in your case, since you did not paid the tax, this amendment is not applicable.
In short, its still possible for you to claim benefit..
Inform employer that he has not followed the provisions of S.192 and hence to the extent of default, by virtue of S.40a, 30% of the salary on which tax was not deducted shall be the disallowance to the employer and the liability for short deduction of tax at source is also payable as per sec 201.
Due to this the employer will have to deduct the tax on salary and employee will receive the credit of the same and hence the tax liability of the employee would be decreased as he would get the credit of that and there shall be consequental decrease in the interest aswell.