Public prosecutors on Thursday arrested former Justice Minister Katsuyuki Kawai and his lawmaker wife, Anri Kawai, on charges of vote-buying during her successful Upper House election bid last summer, further pushing the duo into legal trouble and presenting perhaps the biggest political challenge yet this year to Prime Minister Shinzo Abe.

The couple was ordered to report to authorities early Thursday. They are accused of distributing as much as ¥25 million in total to roughly 100 prefectural and city assembly members in Hiroshima — Anri Kawai’s precinct — ahead of the House of Councilors election in July of last year. It is believed that her husband was essentially running her campaign.

The arrest is a severe blow to the Abe administration, especially because of Katsuyuki Kawai’s closeness to Abe and Chief Cabinet Secretary Yoshihide Suga. He was a former policy adviser to Abe and the head of a caucus in the Liberal Democratic Party that essentially backed Suga.