The largest faction of Japan's ruling Liberal Democratic Party is suspected of funneling all proceeds from sales of tickets to fundraising events into kickbacks to Upper House members in their election years.

Sources say the Abe faction set no quotas on party-ticket sales for Upper House members facing the elections in 2019 and 2022. All the money from the ticket sales is said to have been given to their offices as kickbacks.

The Abe faction, once led by late Prime Minister Abe Shinzo, is believed to have paid kickbacks to the offices of member lawmakers who sold more than their quota of fundraising event tickets.

They are believed to have systematically failed to record the amounts as revenue in their political fund reports, in violation of the political funds control law.

Tokyo prosecutors raided the faction's office last week to shed full light into the practice.

Upper House lawmakers serve a six-year term, with half of the members being elected every three years. Because the timing of Lower House elections is unpredictable, the payments were not made to Lower House members.

The unreported money collected by the Abe faction over a five-year period through 2022 likely adds up to about 500 million yen, or about 3.5 million dollars.

The prosecutors are believed to be investigating how the kickbacks have been used.