Yes, you can. Go to the UFT website at www.uft.org/enrollment-info and fill out the online union enrollment form. You should select the “enroll in the UFT” button to register for a website account (and verify your email address) and then you should follow the “join the union” prompts.
If you have any questions or run into difficulty with the online union enrollment process, please call the UFT Membership Department at 212-701-9690.