When the Accused Has No Armor.

I was wondering what laws exist to protect employees. It seems like employers can accuse employees of anything such as theft or other breaches and the burden often falls on the employee to prove their innocence.But how is someone supposed to prove their innocence in such cases?

Something similar happened to someone I know when they tried to resign, and I also came across a similar incident on Reddit. Being an employee often feels like dealing with harassment on so many levels.