Prosecutors plan to question former Justice Minister Katsuyuki Kawai and his lawmaker wife Anri possibly on Thursday, a day after the current Diet session ends, on suspicion of giving out cash to local politicians and supporters during the wife's campaign in last year's upper house election, sources close to the matter said Monday.

Prosecutors are seeking to press charges against them in violation of the Public Offices Election Law. Lawmakers have special immunity from arrest while the Diet is in session.

The move would deal a blow to Prime Minister Shinzo Abe, given his ties with Kawai, 57, who served as special adviser for foreign affairs to Abe before briefly serving as his justice minister last year.

During several rounds of voluntary questioning, the couple, who belong to Abe's Liberal Democratic Party, have denied vote buying allegations.

Prosecutors have found that Kawai, a member of the House of Representatives, orchestrated the campaign for his 46-year-old wife.

Investigations have found the couple may have handed a total of more than 20 million yen ($186,000) in cash to around 100 people for Anri Kawai's campaign.

The former minister allegedly offered 50,000 yen to over 100,000 yen in cash each to supporters of the couple in their constituencies in Hiroshima Prefecture, prefectural and city assembly members in the western Japan prefecture, as well as local government chiefs.

Anri Kawai, a member of the House of Councillors, was also found to have handed out cash to local voters and others.

In the upper house election last July, the LDP fought for two seats in the Hiroshima constituency by backing Anri Kawai along with veteran lawmaker Kensei Mizote.

But Mizote lost his seat as conservative voters were divided.