If joined by a conjunction, the independent clause is preceded by a comma. When in doubt, follow this guideline. Non-restrictive clauses are parenthetical to the main clause. This clause could be excluded from the sentence without affecting its meaning. It is, therefore, non-restricting.
Restrictive clauses give meaning to the sentence.
If this clause is removed, the meaning of the sentence is changed. The person is told to remove only the boxes. You won't see these or write these very often in journalistic style.