A politically contentious trade bill passed the U.S. Senate on Wednesday evening, handing President Barack Obama "fast-track" negotiating authority for a Pacific trade agreement pending his signature.
The political maneuvering and opinions on the trade partnership remain complex. But the money flowing to senators from interested groups has been much more one-sided.
Industries, such as banks, insurance companies, utilities and many more, that back the bill in its current form have donated $218.4 million to current senators since October 2008, according to money in politics researcher MapLight. That's about nine times more than the $23.2 million contributed by groups that oppose it. (Tweet This)
"As far as business, this is the most important vote that will be taken this year," said Anthony Corrado, a professor of government at Colby College in Waterville, Maine, who studies campaign finance. "The business community for the most part has been united on TPA, so you might expect a large disparity."
Obama and many legislators have called for the president to receive negotiating authority for the 11-country Trans-Pacific Partnership, saying it opens channels that benefit American business. But the plan has received backlash for potential job outsourcing and lax environmental regulations.
The TPA was previously packaged with the so-called Trade Adjustment Assistance, which provides protections and training for workers displaced by jobs moving overseas. After political wrangling, including some opposition from Obama's Democratic Party, the House last week passed a version without TAA provisions.
Senate Majority Leader Mitch McConnell reaps the most from supporters of this version of the bill, taking in $8.26 million since 2008. Among the top 10 recipients, six are Republicans, and four are Democrats.
"A strong dependency for money, in the form of campaign contributions, exists on both sides of the aisle," said MapLight spokeswoman Pamela Behrsin, adding that trade groups are just some of the players who "have the ear" of Congress.
Democratic presidential candidate and Vermont Sen. Bernie Sanders has unsurprisingly received the least money, about $140,000, from backers of the bill. Sanders raises much less money than his peers and much of it comes from labor unions or other groups that often oppose international trade agreements.
Read MoreHillary's campaign stumbles on trade
Corrado noted that some labor unions threatened to withhold campaign contributions to Democrats before the TPA made its rounds through Congress. Still, Corrado said a "great disparity" would have existed even with more labor union donations.
The final vote for fast-track authority comes after the Senate voted 60-37 to advance it on Tuesday. Senators who voted for the Tuesday measure received an average of $2.34 million from trade agreement supporters, 22 percent more than those who voted no.
Senators who voted against it took in an average of $443,254 from industries that oppose it, about four times more than those who voted yes.
Still, the big contributions may not hold that much sway on votes, Corrado said. Many industries probably chose to donate to candidates based on their record, rather than encourage them to change their policy outlook, he noted.