On Tuesday a controversial bill goes up for a vote in the Senate Foreign Relations committee that will test just how much say Congress has on a possible nuclear deal with Iran. When it comes to legislation that would give Congress a final say in approving or rejecting a deal, the Obama administration has been very critical.

Speaking exclusively for the New York Times, Obama said that preventing Tehran from getting a nuclear weapon and moving toward stabilizing the Middle East has been made possible thanks to the newly agreed on framework of a nuclear deal with Iran, which represents a “once in a lifetime opportunity.”

The administration stepped up its lobbying campaign on Capitol Hill on Monday. White House press secretary Josh Earnest said: “We strongly oppose the way legislation is currently written. However, despite that, we still continue to have extensive conversations on Capitol Hill with members of Congress.”

For the purpose of meeting with members of the House to discuss the negotiations, Secretary of State John Kerry postponed a foreign trip. Classified briefings were held with members of the Senate and House on Monday and Tuesday by Kerry, Treasury Secretary Jack Lew, Energy Secretary Ernest Monis and senior officials in the intelligence community.

According to Earnest, some Republicans will reject any deal just because Obama supports it, and are “rigidly partisan.” He also said that administration officials will continue to talk with members of his party, even though there is some Democratic opposition. More than 130 telephone calls were made by the president and other senior administration officials so far to members of Congress in order to discuss the negotiations.