Some people have suggested the right of peaceful assembly and freedom of speech enshrined in the United States Constitution means the City of Portland is not allowed to regulate the time,  place and manner of Occupy Portland's and other protests. 

The foundational U.S. Supreme Court decision on this question was issued in March 1941, in Cox v. New Hampshire.  This case involved a demonstration by Jehovah's Witnesses on a public street without taking out a permit. 

The Court stated (my emphasis):

<< Civil liberties, as guaranteed by the Constitution, imply the existence of an organized society maintaining public order without which liberty itself would be lost in the excesses of unrestrained abuses.  The authority of a municipality to impose regulations in order to assure the safety and convenience of the people in the use of public highways has never been regarded as inconsistent with civil liberties but rather as one of the means of safeguarding the good order upon which they ultimately depend.  The control of travel on the streets of cities is the most familiar illustration of this recognition of social need.  Where a restriction of the use of highways in that relation is designed to promote the public convenience in the interest of all, it cannot be disregarded by the attempted exercise of some civil right which in other circumstances would be entitled to protection.  One would not be justified in ignoring the familiar red traffic light because he thought it his religious duty to disobey the municipal command or sought by that means to direct public attention to an announcement of his opinions.  As regulation of the use of the streets for parades and processions is a traditional exercise of control by local government, the question in a particular case is whether that control is exerted so as not to deny or unwarrantedly abridge the right of assembly and the opportunities for the communication of thought and the discussion of public questions immemorially associated with resort to public places.  

...... If a municipality has authority to control the use of its public streets for parades or processions, as it undoubtedly has, it cannot be denied authority to give consideration, without unfair discrimination, to time, place and manner in relation to the other proper uses of the streets. We find it impossible to say that the limited authority conferred by the licensing provisions of the statute in question as thus construed by the state court contravened any constitutional right.>>

I am struck by the beauty of the prose, as well as the clarity of the decision.  The full decision on the case is posted here.