The charter of the United Nations states that, "All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations."
Under the section regarding the use of force it clarifies that the use of force must be in self-defense or under the authorization of the security council.
Neither or these conditions have been met, thus if the United States take military action in Syria, we will be making a mockery of the very international laws that we profess to be upholding.
No action should be taken without the approval of the Security Council.