House and Senate negotiators are working to strike a difficult balance as they negotiate the final intricacies of the so-called fast-track bill, which would give the president Trade Promotion Authority (TPA).

TPA has been given to all previous presidents since Gerald Ford, with similar authority granted to all presidents since Franklin Delano Roosevelt. In recent weeks the White House has began a significant push on getting Congress to pass TPA and Congress could take up a package as soon as this spring.

A bipartisan group of former U.S. agricultural secretaries sent a letter to Congress calling for support of TPA, saying it “ensures that the U.S. has the credibility to conclude the best deal possible at the negotiating table.”

TPA allows Congress to set negotiating priorities for the administration and provide input, while ensuring a deal struck overseas would get a congressional up-or-down vote on trade deals without amendments or procedural delays. TPA is critical in assuring trading partners they will not be asked for deeper concessions on Capitol Hill after negotiations are complete.

The legislation comes as the Obama administration is seeking to conclude negotiations on a 12-nation Trans Pacific Partnership (TPP) trade deal.

TPA is popular with Republicans but many Democrats, labor unions, and environmental groups oppose the legislation, saying it is a way for the administration to push a deal with unacceptable provisions through Congress. But, including too many provisions friendly to Democrats could alienate Republicans and the business community, or even potentially put TPP at risk when it comes up for a final vote.

The United States, Japan, and 10 other Pacific Rim countries are hoping to agree to the final terms of the TPP in the coming months.

In a newsletter from the National Chicken Council, it was reported that the TPA bill’s authors-Sens. Orrin Hatch (R-Utah), Ron Wyden (D-Ore.) and Rep. Paul Ryan (R-Wisc.) - are now fighting over a crucial remaining issue of how much leverage to give lawmakers to remove any coming trade deals from fast-track protection. Complications on that issue or others could still delay or unravel any agreement, those close to the negotiations said.

Generally, Republicans do not want to insert a mechanism that makes it easier to defeat trade agreements. Republicans say too many levers in Congress could derail a deal or make trading partners such as Japan nervous about putting their best offers on the table. Democrats want more openness and say the current policy prevents Congress from serving as a watchdog over trade deals.

Hatch called a hearing Feb. 26 of the Senate Finance Committee which he chairs to discuss trade policy and potentially the new bill. But his ranking member Wyden, the top Democrat on the panel, said a hearing was “premature” because a final deal had not been struck yet. The hearing ended up being postponed, without a new date set.

NCC said observers say the legislation has a fair chance of getting through the House. Even if 40 Republicans voted against the bill, the measure could still pass with just a dozen Democratic votes. In the Senate, the 60-vote threshold could be met if Wyden and other crucial Democrats came on board.

Democratic opposition blocked a fast-track bill last year, and some critics of the administration’s policy say the latest bill probably will not change the level of support in President Obama’s party.

Free trade agreements have proved to reduce barriers to U.S. exports and expand market opportunities. In 2014, 47% of U.S. goods exports went to countries the U.S. currently have FTAs with, and exports to FTA partners are up 64% since 2009 whereas exports to the rest of the world have gone up just 45%.

For a graphical look at the impact of U.S. trade relationships, view this Benefits of Trade Agreements document put together by the International Trade Administration.