Seoul — From next year, the members of South Korean boy band BTS will have to start serving in their country's military. It's a major blow for the group's die-hard fans, who launched an appeal to have the seven young men spared from their country's mandatory military service.

BTS, or "Beyond the Scene," have captured the hearts of millions of fans around the world, topping music charts, selling out worldwide stadium tours and winning myriad awards — including Billboard Music Awards and American Music Awards.

Earlier this week, South Korea's Minister of Culture, Sports and Tourism, Park Yang-woo, said he wanted to grant the seven mega-celebrities an exemption from the draft.

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But on Friday, the ruling came down: The Ministry of Defense said it had reviewed a request to change the rules that would have allowed BTS to keep touring the world under a conscription waiver "but we decided that the system needs to be continued."

In other words, BTS will have to serve just like everyone else. The ministry said changing the rules for pop stars could have "a huge impact on the promotion of people's morale and enhancement of national character."

Mandatory service

Fighting in the Korean War ended in 1953, but it ended with an armistice rather than a peace treaty. That means South Korea technically remains at war with North Korea. There are about 28,000 U.S. troops still based in the South to bolster the close American ally's defenses.

Given those circumstances, every healthy Korean man is obliged to serve in the military before turning 28. The majority serve for 18 months.

Waivers are granted for people with certain skill sets, including professional athletes and even some celebrities who are deemed to contribute to their nation in other ways — but not, according to the decision made this week, pop stars.

The draft can be a major obstacle for music groups, especially boy bands. Any delay in production can make it hard for a group to keep up with ever-changing trends, and for fans, the rougher image associated with military service can seem at odds with the themes of K-pop.

Given the range of ages of members, it can take years for a boyband to try to regroup. The members of another South Korean boyband, Super Junior, took turns putting their careers on hold over the span of an entire decade while they completed their mandatory service.

A "natural" duty

The oldest member of BTS turns 28 next year.

The looming deadline prompted worried members of BTS' die-hard fan base, known as the ARMY (which stands for "Adorable Representative M.C. for Youth"), to launch a petition on the website of the Blue House, the South Korean presidency.

They argued that BTS has already served their country by promoting K-pop far beyond South Korea's borders and helping to lure tourism back to the country in the process.

But even among members of the ARMY (the fan club, not the one with the guns), there was clearly some recognition that dodging the draft is an unpopular move. In spite of BTS' enormous popularity, only about 6,100 people signed the petition.

Not long after that petition appeared, a counter-petition hit the presidential website.

"Just because they were on the news, what right do they have to be exempt from the military?" the new petition asked.

Speaking to CBS News earlier this year about the prospect of military service, the BTS member facing the first call-up, Jin, said as a Korean, serving in the armed forces was "natural."

CBS News' Seth Doane interviews South Korean boy band BTS. CBS

"Some day when duty calls, we will respond and do our best," he said. For him, that's next year.

"We don't want to think about it," said another member in the April interview with CBS News' Seth Doane. He said they know they have a good thing going and they just want to live in the moment.

While South Korea's army will soon have some high-profile new recruits, the ARMY has been dealt a double blow this week; not only will their pop idols have to trade microphones for rifles, but the band was also passed up this week for a Grammy nomination.

BTS wrapped up their Love Yourself World Tour in October. Their next performance in the U.S. is at the Jingle Ball on December 6 in Los Angeles.