Here is a bilateral action: sitting down with a negotiating partner and agreeing on a joint means of solving a problem. Here is a unilateral action: attempting to "solve" a problem on your own. By that definition "settlement" is a unilateral act. So is "annexation". So if "confiscation". But going to the UN is not a attempt to "solve" a problem unilaterally. It is what it is i.e. an appeal for outside arbitration.
U.S. Democratic Sen. Bill Nelson announces support for Iran nuclear deal (Haaretz)