TOKYO (Reuters) - Japanese opposition lawmakers on Friday urged a former finance official to testify in parliament about a suspected cronyism scandal that could pose a risk to Prime Minister Shinzo Abe’s support and hurt his push to revise the pacifist constitution.

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Suspicions that a school operator with ties to Abe’s wife, Akie, got a sweetheart deal on land for a school in the western city of Osaka helped erode the premier’s popularity last year. The former head of the school operator and his wife were arrested in July on suspicion of illegally receiving subsidies.

Abe, who has repeatedly denied that he or his wife did favors for former Moritomo Gakuen head Yasunori Kagoike, subsequently led his ruling coalition to a sweeping election win in October and his ratings have recovered to around 50 percent.

Revelations that the finance ministry had kept documents about the sale of government-owned land to Moritomo Gakuen have reignited concerns over the affair. Last year, Nobuhisa Sagawa, then the head of the ministry’s financial bureau, told parliament the materials had been discarded.

Five opposition party lawmakers visited the finance ministry to ask Sagawa, now head of the National Tax Agency, to appear in parliament, but were told he was not available to meet them. They submitted a letter with their request.

As they made their demand, about a thousand people gathered in front of the ministry, carrying placards with slogans such as “Let’s expel Abe, (Finance Minister Taro) Aso and Sagawa”.

“Are you in this building? Why can’t you come out and greet the taxpayers, instead of hiding yourself sneakily?” said Satoshi Daigo, an emeritus professor at the University of Tokyo.

While the simmering scandal is unlikely to pose any threat to Abe’s grip on power, an erosion of his support could undermine his campaign to achieve his long-held goal of revising the war-renouncing, post-war constitution.

“It’s a fire you cannot put out,” said Jesper Koll, head of WisdomTree Japan, an equity fund. “Does it undermine Abe’s credibility? It does.”

Abe wants to build a lasting legacy by revising the constitution’s Article 9 - which, if taken literally, bans a standing military - to make clear that Japan’s armed forces are constitutional, although successive governments have already interpreted the clause to allow a military for self-defense.

Constitutional amendments must be approved by two-thirds of both houses of parliament and a majority of voters in a public referendum, which could hinge as much on how voters view Abe as the revision itself.