Company pays you for non use of certain amount of sick days
Can these sick days be taxed as bonus

Can end of year sick days be taxed as BONUS

Is this a separate payment from your regular paycheck? If so, then it seems logical - how else would you do it? I would expect that deductions would be taken for federal and state/local taxes, FICA, and employee contribution to 401(k) if applicable. But not deductions for things taken out of regular pay on a monthly basis, such as medical, dental, life insurance.

Duplicate question - see: https://www.askmehelpdesk.com/taxes/sick-days-taxed-bonus-455826.html

We receive a separate check at the end of the year for unused sick days

Can the company consider this check as a BONUS and withhold more % of taxes or is this check to be taxed based on regular monthly taxes

Checks received net was at least 1/2 of the Gross

Company is in NYC

Typically bonuses have tax withheld at 25% for federal tax purposes. Is that what they did? If you're concerened that too much is being withheld, just remember that you'll get a bigger refund once you file your tax return.