Only Congress.
The legislative branch, specifically the Senate in the United States, has the authority to reject treaties. According to the U.S. Constitution, a two-thirds majority vote in the Senate is required for a treaty to be ratified. If the Senate does not approve a treaty, it cannot be enacted, effectively rejecting it. This role ensures that treaties receive significant scrutiny before becoming binding agreements.
The Senate has the responsibility of approving treaties.
The Constitution requires the Senate to ratify treaties. Until the Senate approves them, they are not in force. The Senate does not automatically approve all treaties that the President sends to them.
ratify
Referendum is a right reserved to the people to approve or reject an act of the legislature, or the right of the people to approve or reject legislation that has been referred to them by the legislature.
The US Congress needs to approve treaties the US becomes parties or signatories of. I'm not sure what you mean by UN treaties, however.
Only congress can.
The Senate must approve treaties and presidential appointments.
They must meet with the other countries, work out the details and agree to it, finalize the treaty into a bill of sorts, and the Senate must confirm it with a vote of 2/3. Pretty cut-and-dry.
The Senate is responsible for either approving of a treaty or rejecting it.
disapprove, turn down, reject, veto, disallow
Legislative