An estimated 670,000 workers on Wednesday took part in May Day rallies at around 450 locations across the nation, calling for government measures to secure workers' rights and improve the worsening employment situation, organizers said.
The rallies were organized by the National Confederation of Trade Unions (Zenroren) and affiliates of the Japanese Trade Union Confederation (Rengo).
Zenroren held its main gathering in Kameido Park, Tokyo, drawing an estimated 80,000 people, according to the organizers.
With unemployment hovering at record highs, Zenroren protested pay cuts and layoffs.
"The unemployment rate and the number of small and medium-size enterprises going bankrupt is really serious," Yoji Kobayashi, head of the organization, told participants at the rally.
"Prime Minister (Junichiro) Koizumi's government is not taking any effective measures to tackle economic problems, but only making the economy worse. Koizumi is not capable of leading the government."
Rengo, the nation's largest labor group, and most of its affiliates staged rallies across Japan on Saturday, with about 181,400 people attending at 137 venues in 35 prefectures.
Rengo began holding May Day rallies on the first day of the Golden Week holidays a year ago in an effort to increase participation and draw more attention to the events.
Labor groups not affiliated with Rengo or Zenroren assembled at Hibiya Park, also in Tokyo, for a rally led by the National Trade Unions Council (Zenrokyo).