The House of Representatives endorsed a bill Thursday to change the name of Greenery Day, a national holiday that currently falls on April 29, to Showa Day.
The bill would also see May 4, another national holiday, celebrated as Greenery Day.
The legislation to amend the National Holidays Law cleared a Lower House plenary session thanks to support from lawmakers of the three ruling parties, the Democratic Party of Japan and the Liberal Party.
Debate in the House of Councilors is expected to be carried over to the next Diet session, due to a shortage of deliberation time. The current session is slated to end July 28.
Although DPJ members who used to be members of the Socialist Democratic Party voiced strong opposition to the bill, the DPJ decided at an executive meeting Tuesday to support the measure.
But four DPJ lawmakers did not toe the party line. Kinya Narazaki opposed the bill by not standing up during the vote, while Ken Okuda, Yukio Ubukata and Yutaka Kuwabara left their seats before voting.
April 29 was Emperor Showa's birthday. After his death in January 1989, his birthday, already a national holiday, was designated to continue as such under the name Greenery Day.
May 4 is a specially designated holiday that creates a longer Golden Week vacation period, falling as it does between Constitution Day on May 3 and Children's Day on May 5.