The outspoken businessman, who is known to start brawls on Twitter, sent out a series of tweets explaining his opposition.
"The Trans-Pacific Partnership is an attack on America's business. It does not stop Japan's currency manipulation. This is a bad deal," he said.
[by Alanna Petroff | April 23, 2015 | CNN Money]
It hopes to wipe out trade tariffs to bring down the cost of importing and exporting, which would help make U.S. businesses more competitive overseas. It would also make it easier for businesses to invest in other countries.
The U.S. government estimates a TPP agreement would add $223 billion per year to the global economy by 2025.
But Trump believes the deal would hurt U.S. businesses, particularly manufacturers, and put people out of work.
Trump's line of thinking goes like this: U.S. firms would be hurt if the free trade deal makes foreign products cheaper for Americans to buy.
He notes Japan's recent record of devaluing its currency, which makes it easier for Japanese exporters to compete for U.S. business.
According to data from 2012, America's trade with the 11 other nations was worth roughly $1.8 trillion, up 46% over the previous three years.
The government estimates that trade with these countries has helped support four million American jobs.
The U.S. government is also working on a similar deal with the European Union, called the Transatlantic Trade and Investment Partnership.