South Korean activists and conscientious objectors to military service are seen during a rally outside the Constitutional Court in Seoul on June 28.
Seoul, South Korea CNN  — 

South Korean authorities have vowed to “make an example” of 12 music students accused of conspiring to gain weight to avoid mandatory military service.

South Korea’s Military Manpower Administration said the group had exchanged messages on KakaoTalk, a social messaging app similar to WhatsApp, about how to gain weight quickly.

Some of them reportedly consumed large amounts of protein powder, while others drank a thick aloe beverage on the day of their exam to appear heavier than they actually were.

“The Military Manpower Administration, via thorough investigation, will do our best to root out military service evasion crime and make an example of the violators so that a fair and just military service culture can take root,” authorities said in a statement.

South Korea – which is still technically at war with North Korea – requires all men between the ages of 18 and 35 to perform at least 21 months of military service, though the country’s Defense Ministry has pledged to reduce the term to 18 months by 2020.

Conscription requirements are based on a combination of height, education and body mass index. Authorities also consider factors such as eyesight, disability and criminal history.

The students, who have not been named, are all vocal music majors at the same university in Seoul. They feared that being assigned to active duty could interrupt their careers, and that a better option would be to serve as social service personnel – working for the government in a non-military capacitywhich would give them more time to practice, authorities said.

Social service duty is assigned to those who are unable to enroll in the military for health reasons.

The Military Manpower Administration said the music students, if convicted, must receive criminal punishment, get re-examined and then serve in the military again. Two of the 12 had already finished their social service duty.

03:33 - Source: CNN
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Though mandatory conscription is popular with conservatives in South Korea, critics say the law can ruin careers, and claim it violates the human rights of people who refuse military service based on deeply held religious beliefs.

Young men have previously been known to get full body tattoos or harm themselves in order to get an exemption, according to Yonhap news agency.

Others have been known to try to add on or tack off pounds to avoid conscription, so the government conducts surprise inspections for anyone suspected of changing their weight.

Conscientious objection is not currently permitted, and those who decline to serve often face prison time.

South Korea imprisons more people for conscious objection than the rest of the world combined, according to Amnesty International. Hundreds are jailed each year, the rights group says, many of whom are Jehovah’s Witnesses who refuse to serve due to their religious beliefs.

But that is expected to change in the coming months, as the country’s Constitutional Court ruled in June that the country must provide alternative civilian roles for those who refuse to take up arms due to religious or political reasons.

CNN’s James Griffiths contributed to this report