Growth in gross domestic product could be pushed down by 1.0 percentage point, or ¥4.8 trillion, if Japan joins the envisaged Trans-Pacific Partnership, a group of researchers said Wednesday.

The estimate, covering the impact of eliminating tariffs on farm products and increasing exports to other countries, contrasts with a government estimate in March that the pact could boost growth by 0.66 point, or ¥3.2 trillion.

The researchers, who oppose the TPP, said their efforts to reflect the pact's impact on not just the farming sector directly but also industries related to farming accounted for the difference.

During their presentation in Tokyo, Eiji Doi, an honorary professor at Shizuoka University, also said farming output would fall by ¥3.5 trillion, and as many as 1.9 million people, mostly farmers, could lose their jobs if Japan joins the TPP.

Japan is set to become in July the 12th nation to join the talks over the free-trade pact. The participating countries hope to conclude the deal by the end of the year.

Farmers protected by high tariffs fear an influx of cheap imports.