Kawasaki Frontale were fined $15,000 and placed on one-year probation by the Asian Football Confederation on Thursday after their fans raised a controversial wartime Japanese flag during a recent Asian Champions League match in South Korea.

If the flag reappears during their probationary period, Kawasaki will automatically be forced to play one game in front of an empty stadium.

The AFC's disciplinary committee, which found Frontale guilty on charges of discrimination and spectator misconduct, notified Frontale through the Japan Football Association.

Kawasaki's next AFC-sanctioned match is on Tuesday in the ACL at home to Hong Kong's Eastern SC. Toru Oniki's men can qualify for the round of 16 with a win over Eastern.

Should they violate their probation, Kawasaki will be the first Japanese side to host a match at an empty stadium in an international competition, according to the JFA.

Kawasaki were charged by the AFC last week, and had been waiting for word on their punishment from Asian soccer's governing body.

Frontale could be considered fortunate as Article 58.3 of the AFC's disciplinary and ethics code states a team could face a minimum penalty of playing two matches in an empty stadium plus a fine of at least $15,000.

In March 2014, the J-League ordered Urawa Reds to play in front of an empty stadium against Shimizu S-Pulse after their fans put up a banner at Saitama Stadium that read, "Japanese Only."

In Kawasaki's 1-0 win at Suwon Bluewings on April 25, two Frontale supporters waved the 16-ray rising sun flag, nearly provoking a post-game riot.

Kawasaki officials confiscated the flag from the two fans and had to escort other supporters out of the stadium.

The flag was used by the Imperial Japanese Army during World War II. Although it is still flown by the Japan Maritime Self-Defense Force, the flag is considered a symbol of Japan's wartime aggression in many Asian countries, including South Korea and China.