Law enforcement sources tell TMZ ... Laguna Beach PD has put the word out to the organization ... there is a "zero tolerance policy" for Sunday's rally, where demonstrators will demand tougher border policies. Cops have said they will not give warnings on Sunday ... demonstrators who go where they should not go or break the law by fighting, throwing objects or inciting violence will go to jail.

The cops are making something else clear ... their no tolerance policy applies to all sides ... people demonstrating and people protesting the protesters.

The Department has reviewed other recent demonstrations that got out of hand, and it's concluded that warnings don't nip things in the bud and it's harder to get things back under control.

The LBPD says they are in full support of the First Amendment. People can demonstrate as long as they obey the law and the rules. They want to make sure the town still functions around the demonstration, and anyone who tries to disrupt will get a new set of cuffs.