I am on intermitent FMLA at work. My employer has changed my job description to include a task that he knows I am on restriction from doing

If this new task is not part of the original job description or, even if it may arguably be part of your duties but was never or rarely performed before you took FMLA, then it appears that the employer is now retaliating against you for taking FMLA leave.  This would constitute illegal retaliation under the FMLA.  If this new assignment is not an essential job duty, then you can also ask for a reasonable accommodation under the ADA with respect to this new task.  You should also meet with an employment law attorney ASAP as it seems that the employer is looking to terminate you