(Bloomberg) -- The Japanese Communist Party more than doubled its seats in the lower house of parliament as its pacifist, anti-nuclear platform provided the clearest opposition to Prime Minister Shinzo Abe’s policies.

The JCP won 21 seats in yesterday’s lower-house election, up from 8 before the vote, even as the ruling coalition maintained its two-thirds majority. The Communists won their first single-seat district in 18 years, claiming a seat in the southern Okinawa island chain. The party can now submit legislation to parliament.

The Communists have called for a sales-tax increase planned for 2017 to be scrapped and for Japan to stay out of the Trans-Pacific Partnership, a regional trade agreement favored by Abe. Party leader Kazuo Shii has opposed restarting nuclear power plants closed after the 2011 Fukushima disaster, as well as the reinterpretation of the U.S.-imposed pacifist constitution to allow Japan to defend other countries.

“It’s the only opposition party that really acts like one,” said Tomoaki Iwai, a professor of politics at Nihon University in Tokyo. “It will be the choice of disgruntled voters.”

Established in 1922, Japan’s Communist Party was initially an illegal organization whose leaders were persecuted for opposing Japan’s aggression in Asia. Re-established on a legal footing after the war, its parliamentary representation peaked in 1979 at 39 seats when it opposed the introduction of a flat sales tax.

“I wanted to stop the LDP,” said Kazuko Takahashi, an 84-year-old pensioner living in Tokyo, who said she voted for the Communists because she was worried about changes to the pacifist constitution. “I don’t want another war. My generation still remembers the war, and I can’t let things return to that.”

The party has called for an increase in income tax in place of the sales tax increase to help rein in the world’s largest debt. It also seeks to stop the construction of a new U.S. military base on the island of Okinawa.

To contact the reporters on this story: Isabel Reynolds in Tokyo at ireynolds1@bloomberg.net; Maiko Takahashi in Tokyo at mtakahashi61@bloomberg.net

To contact the editors responsible for this story: Andrew Davis at abdavis@bloomberg.net Andy Sharp, Neil Western