Federal, State (NY & CT) and City (NYC & Yonkers) tax withholding elections can be done through the self service portal www.mymta.info
Click on the link above to enter the portal with your BSC ID and password. On the home page click on MY PAY. There is a separate link for each tax. Click on the link to make changes. Before changing your NY or CT State withholding click on the blue icon on the right to read instructions.
Only NY & CT residents can change their State withholding elections, Only NYC & Yonkers residents can make changes to their City withholding elections.