I think you may be misunderstanding the purpose of the notice you have received. Apparently Form LO 400, Notice of Potential Charges is a way for the Dept. of Labor to allow you to correct errors that might lead to your experience rating to change based on payment of benefits to a former employee who was not eligible to receive them, or to prevent your experience rating from being raised by benefits improperly charged to your account. It is not a bill for the benefits themselves, which are paid from the insurance fund. Your insurance premium amount is in part determined by how much the fund has paid to your unemployed former employees. If you have a bunch of them drawing benefits (your experience) your premium will increase. So if you can avoid having these benefits charged against your account, your premium next year will probably be lower. The actual money is not withdrawn from your account, but the bookkeeping debit will affect your experience rating and hence your premium in the future. "For every employer liable for contributions, an individual account is set up as a bookkeeping device for measuring the employerπs account percentage, which is used in determining the tax rate."
http://www.labor.state.ny.us/ui/PDFs/ia31812.pdf Apparently you are being notified because your former employee is using his service with you to qualify for benefits, even though you are not his most recent employer.
"Q: Why is there a charge to my account? An employee left my company some time ago under conditions that should disqualify them from receiving benefits.
A: We base a claimant’s eligibility to receive benefits on the reason for separation from the last employment prior to filing the claim. For claims effective January 6, 2014 or later, any employer may protest charges to its account based on a claimant’s reason for separation, such as misconduct or voluntarily leaving without good cause. We must receive the protest within 10 calendar days of the Notice of Potential Charges.
Charges to your account are correct if:
• You do not protest in a timely manner, or
• The reasons for the employee leaving were not disqualifying
For questions, contact the Telephone Claim Center at (888) 890-5090"
https://labor.ny.gov/ui/employerinfo/experienceratingfaq.shtm#0