I think there is no confusion in your query, but in the answers. In Karnataka, the professional tax of ₹2,500 per annum is to be paid for each location situated within Karnataka. In other words, if a Pvt. Ltd. or Ltd. company has no branch offices within Karnataka, such a company has to pay ₹2,500 per year as an employer registration fee. If any Pvt. Ltd./Ltd. company has different branch offices within the state of Karnataka, in such cases, the company will pay ₹2,500 as an employer registration fee for each location.
From the answers, it seems most of the respondents are confusing employee contribution of PT and Employers' registration fee. You could have mentioned the location of your office to avoid the above confusions.
Regards,
Nair