The agreement provides a right to be consulted for any large consumptive takings or exports from the basin, and a right to be heard. It provides certain legal remedies. It would not constitute a veto power, but it does allow you to be heard. It's a reciprocal process, so each of the states and the two provinces have granted that privilege to each other, to act in the best interests of the watershed.
On March 4th, 2014. See this statement in context.