Japan’s new prime minister Yoshihide Suga has become embroiled in his first scandal after refusing to confirm the nomination of six professors to an advisory council, in apparent retaliation for their political views.

The Science Council of Japan, an independent public body that represents the country’s academic community, has demanded an explanation for the unprecedented rejection of its candidates by the prime minister’s office, which has the formal power of appointment.

Rejection of the professors risks an early end to the prime minister’s honeymoon period and will highlight Mr Suga’s reputation as a hard-nosed powerbroker, undermining recent efforts to soften his image.

Opinion polls have given Mr Suga approval ratings of greater than 70 per cent since he took over from Shinzo Abe last month. But according to a poll by the Japan News Network, the public said he was wrong to reject the nominees by a majority of 51-24.

Appointments to a scientific body should not be politicised, said Jun Azumi, head of parliamentary affairs for the opposition Constitutional Democratic party. Calling for ministers to answer questions in the Diet, he said: “Someone in the cabinet needs to explain why Mr Suga has departed from that.”

Candidates for the body are normally chosen by the academic community and waved through by the government, but the prime minister’s office unexpectedly rejected six out of 105 candidates, without giving any reasons.

The six rejected scholars included three lawyers, two historians and one theologian. Several were public opponents of the security law passed by Mr Abe’s administration in 2015, which allows Japan to come to the defence of US forces if they are attacked.

One of the six, Takaaki Matsumiya, a Ritsumeikan University law professor, gave parliamentary testimony against a conspiracy law passed by the Abe government in 2017. In comments to local media, he described the decision to reject appointees to the council as a threat to academic freedom.

Opposition leaders said the decision was against the law while Mr Suga’s government insisted it was legal. Katsunobu Kato, the chief cabinet secretary, said the Science Council received ¥1bn ($9.5m) a year in public funding and its members are public servants.

The Science Council has about 2,000 members and its main role is to advise the government on policy issues via a range of committees.

The scandal broke as the Suga administration began the debate on a new fiscal stimulus to take effect next year. Analysts suggest the package could be about ¥15tn and include the extension of coronavirus wage and rent subsidies as well as new cash handouts to households.

It would be Japan’s third supplementary budget for the year to March 2021.