My employer has been deducting money from my pay that I have not authorized. What are my legal recourse if they do not rectify this?

Employers who offer 401k plans are allowed to adopt automatic enrollment. This means the employee will automatically have a certain percentage of their pay placed in the 401k plan unless the employee affirmatively "elects" to stop or change the amount. The employer is not required to change this amount until you provide them with the required notification that you want to stop or change the amount it is usually a form you have to complete or a process that complete via a website.  If you go through this process and they do not change it, then you can contact the US Department of Labor's, Employee Benefits Security Administration.