The Constitutional Democratic Party of Japan, the largest opposition party in parliament, submitted a bill to the Lower House on Wednesday that would allow married couples to retain different surnames — the first step in what’s set to be a long debate over the next two months.

The party will now attempt to coalesce a united front against the ruling coalition in cooperation with other opposition parties. However, a clear divide emerging within the opposition camp suggests that further compromise might be necessary on the road to approval.

The CDP’s bid reflects the party’s endeavors to find some common ground with other actors in parliament, CDP Upper House lawmaker and party acting leader Kiyomi Tsujimoto told reporters after the bill’s submission.

“This is one of those reforms Japan hasn’t implemented for 30 years,” Tsujimoto said. “Without dual surnames, this country will see no progress.”

The proposal harks back to a report submitted by an advisory panel to the Justice Ministry in 1996 — widely seen as the starting point of an almost 30-year-long discussion. That report suggested a revision of the civil code to allow married people to retain their original surname even after marriage.

Unlike a previous proposal the party drafted in 2022 — which assumed parents would decide their children’s surname at the moment of birth — in an effort to garner wide consensus across the aisle, the CDP’s latest proposal specifies that decisions should be made when the couples get married.

Asked why the CDP opted to submit the bill on its own without other opposition parties, Tsujimoto said the CDP has so far explained its proposal to both ruling and opposition parties, and it’s now open for further discussions in parliament.

The divergence of opinions within the opposition camp is likely to give the CDP some headaches, potentially leading to protracted parliamentary debate.

Last week, Nippon Ishin no Kai formulated its own proposal, opting for legally expanding the use of a person's surname before marriage — a possibility supported by portions of the ruling Liberal Democratic Party — rather than introducing a dual surname system.

The party, which retains 38 seats in the Lower House, is expected to formally submit the proposal in the upcoming weeks.

Meanwhile, the Democratic Party for the People has yet to formally present its stance on the subject. In the last general election, the party campaigned on a legal review of the current norms, but party leaders have recently shown a more cautious approach.

“The political world has the responsibility to recognize the desire, shared by many people, to retain their maiden name with legal effect after getting married,” DPP leader Yuichiro Tamaki told a news conference last week, avoiding any clear commitment.

Speaking right after Tamaki, DPP Upper House lawmaker Takae Ito underlined the importance of observing the party’s pledge to voters in the last election.

The ruling coalition has also yet to find a clear consensus on the policy.

While Komeito has long been in favor of allowing double surnames, the LDP is grappling with deep internal divisions between those in favor of a full-fledged review of the law and those advocating to maintain the current legal framework, while expanding the legal use of premarriage surnames.

The debate within the party is expected to resume in May.

Japan remains the only country in the world mandating that couples use one surname after marriage. Justice ministry data shows that in over 95% of cases, the wife takes the name of the husband.