That is from article 2, section 2 of the United States Constitution. Here is the full text:

He shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur; and he shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Ambassadors, other public Ministers and Consuls, Judges of the supreme Court, and all other Officers of the United States, whose Appointments are not herein otherwise provided for, and which shall be established by Law: but the Congress may by Law vest the Appointment of such inferior Officers, as they think proper, in the President alone, in the Courts of Law, or in the Heads of Departments.

So he needs 2/3rds of the present Senators to concur in order to enter any treaty. Well lawmakers are starting to question his deal with Iraq to keep troops there indefinitely:

But there is now also growing alarm about the constitutional issues raised by Bush’s plan. Legal specialists and lawmakers of both parties are raising questions about whether it would be unconstitutional for Bush to complete such a sweeping deal on behalf of the United States without the consent of the legislative branch.

So this is yet another example of how Bush is trying to ignore the law of the land in order to do what he wants. Will Congress act upon this breech of duty? Will they at least try to defend the very basis of our nation – the constitution? I doubt they will with Nancy Pelosi running things.