Anyone who maintains an office in Connecticut or who transacts business within this state and is considered an employer for federal tax purposes is an employer for Connecticut tax purposes and must withhold Connecticut income tax. An employer must register with the Department of Revenue Services by completing REG-1, Business Taxes Registration Application. This application is also used to register for most other state business taxes, including the sales and use taxes, business entity tax and corporation business tax.
Withholding Tax - Nexus