Writing in the New York Times, recently retired NATO commander James Stavridis urges the alliance to lead the charge in Syria—and he sees no legal obstacles to its doing so:
Such action could be justified based on self-defense, owing to the threat posed to Turkey, a NATO member that has backed Mr. Obama’s call for an American-led intervention; the overall threat posed by weapons of mass destruction; and, more controversially, on the evolving international doctrine of a “responsibility to protect.” NATO has not moved forward so far, because of the absence of a United Nations Security Council resolution authorizing action against Syria, but that is not required under the rules of the alliance — indeed, NATO has previously acted with force without such approval, notably in Kosovo in 1999.
Whatever one thinks of the policy merits of his argument, his legal reasoning is thin. The self-defense argument on behalf of Turkey is a stretch, and Stavridis is reaching even further when he claims that NATO's rules don't require Security Council approval. In fact, the drafters of the North Atlantic Treaty went to great lengths to emphasize that the treaty doesn't alter members' obligations under the UN Charter. Article 7 of the treaty reads as follows:
This Treaty does not affect, and shall not be interpreted as affecting in any way the rights and obligations under the Charter of the Parties which are members of the United Nations, or the primary responsibility of the Security Council for the maintenance of international peace and security.