People hold placards and shout slogans as they protest against Japan's Prime Minister Shinzo Abe's security bill outside parliament in Tokyo August 30, 2015. [Photo/Agencies]

A group called Mothers Against War started in July and gained supporters rapidly via Facebook. It collected nearly 20,000 signatures of people opposed to the legislation, which representatives tried unsuccessfully to submit to Abe's office last Friday.

"I'm afraid the legislation is really going to reverse the direction of this country, where pacifism was our pride," said a 44-year-old architect who joined Sunday's rally with her 5-year-old son. She identified herself only as A. Hashimoto, saying politics is still a sensitive topic among parents at her son's kindergarten.

"I feel our voices are neglected by the Abe government," she said.

The bills would permit the Self Defense Force to engage in combat for the first time since World War II in cases of "collective defense," when Japan's allies such as the US are attacked, but Japan itself is not.

The upper house is currently debating the bills, and is expected to approve them sometime next month. But even if it doesn't, the legislation will be sent back to the lower house for a second vote that, if passed, would make it law.