Photo/IllutrationPrime Minister Shinzo Abe enters the prime minister's office on Dec. 6. (The Asahi Shimbun)

A majority of Japanese firms want long-serving Prime Minister Shinzo Abe to finish his term to September 2021 but fewer than one in five say he should stay beyond then, a Reuters poll showed, as allegations that he broke campaign laws erode public support.

Opposition lawmakers allege Abe favored supporters with invites to an annual state-funded cherry-blossom viewing party and may have broken campaign laws by subsidizing backers’ attendance at a reception the night before. Questions have also arisen over whether a gangster attended the state-funded event and why this year's invitation list was shredded.

The prime minister has denied any wrongdoing.

Abe, who quit after a troubled 2006-07 term and returned to office in December 2012 promising to revive the economy, in November became Japan's longest serving premier, breaking a record set over a century ago.

"A lengthy administration invites concentration of power and corruption may easily emerge, but there is no other politician with the experience and ability," a manager at a textile firm said in a written response explaining why Abe should stay on.

Fifty-nine percent said Abe should complete his term as Liberal Democratic Party (LDP) leader but then step down. Another 16 percent want him to stay longer.

That would require a rule change by the LDP, whose head is virtually assured to be named prime minister if the party stays in power.

Twenty-five percent, though, said he should quit sooner.

"Domestically, there is a feeling of stagnation and friction with neighboring countries has emerged," wrote a manager at a transport-equipment firm.

Japan's relations with U.S. ally South Korea have chilled due to a feud over their shared wartime legacy, although ties with China have improved.

Media polls have shown the cherry-blossom affair chipping away at voter support, although backing for the fragmented opposition remains weak. A Mainichi newspaper survey published Monday showed a six point drop to 42 percent from October.

The decline has not ended speculation that Abe might call a snap Lower House election to renew his mandate.

Former defense minister Shigeru Ishiba, an outspoken Abe critic, topped the list--barely--of lawmakers respondents want to take over as prime minister when Abe's term ends, with 17 percent to Abe's 16 percent. LDP rising star Shinjiro Koizumi was the choice for 11 percent.

The corporate survey, conducted from Nov. 20 to Dec. 2 for Reuters by Nikkei Research, canvassed 502 big and midsize nonfinancial companies. Roughly 240 firms answered questions on politics on condition of anonymity to express opinions freely.