SEOUL — Five years ago, South Koreans began calling a number in Britain in droves. They were trying to sway an international phone poll to name Jeju Island in South Korea — a verdant spur of volcanic rock famous for its fresh air and succulent seafood — one of the “new seven wonders of nature.”

South Koreans, from then-President Lee Myung-bak to schoolchildren, pitched in. On Jeju Island alone, government officials voted up to 2 million times a day on their office phones, generating $20.3 million in phone bills.

But Lee Hae-gwan smelled something fishy. Mr. Lee, a union leader at South Korean’s main telephone company, heard from fellow workers that their employer was handling the calls locally, even as it charged South Koreans millions for calling Britain.

Mr. Lee blew the whistle — and paid for it. Over the past four years he has endured a suspension, a transfer, a pay cut and being fired. All, he says, were the result of his whistle-blowing.

His plight — which ended only this year, when he won his job back — demonstrates why South Korea is having trouble getting inside executives and officials to call out wrongdoing, despite a broader push to uproot corruption.

“I would do it again,” Mr. Lee said. “But if my children or friends ask me what to do in the same situation, I would not encourage them to do as I did. You pay too big a price.”

Corruption is becoming a pressing issue in South Korea as economic growth slows and its people begin to demand higher standards from their leaders and big companies. After a string of corruption scandals that implicated prosecutors and judges, opposition parties are calling for the establishment of an independent agency to investigate graft among senior public servants.

A new law went into effect in September that, among other things, bans public servants, schoolteachers and journalistsfrom getting free meals worth more than $27 to prevent conflicts of interest. Meanwhile, prosecutors are increasingly examining the conduct of corporate executives.

Crucial to those efforts, say supporters, is empowering whistle-blowers. Already the government encourages tattling by camera-toting bounty hunters who collect evidence of petty crimes as well as serious infractions like bribery. The Horuragi Foundation, a civic group, and others are lobbying Parliament to extend coverage from current whistle-blower protection laws, which are not as broad as in the United States and elsewhere.

But the groups expect progress to be slow because of broad political gridlock as well as entrenched attitudes toward whistle-blowers, especially among government officials and corporate executives.

“They do whatever it takes to find an excuse to expel whistle-blowers,” said Lee Young-kee, a lawyer who heads the Horuragi Foundation.

South Korea’s past military dictatorship spawned a rigidly hierarchical office culture that made whistle-blowing difficult. With “loyalty to the organization” upheld as a key value, whistle-blowing was seen as an act of betrayal. Rules were routinely ignored in the name of meeting management goals, but few spoke out against colleagues because life in the office revolved around hometown, family and school connections, reinforced through nepotism and late-night wining and dining.

In its 2013 survey of 42 whistle-blowers, the Horuragi Foundation found that 60 percent were fired after exposing corruption in their organizations. Whistle-blowers reported financial straits, divorces and suicidal impulses as they were ostracized by their colleagues and harassed with defamation and other lawsuits from managers. Their names were blacklisted, making it hard to find jobs in their profession, the survey said.

In 1992, in one of the first cases of whistle-blowing in a democratized South Korea, an army lieutenant revealed vote-rigging within the military barracks during parliamentary elections. He was demoted to private and dishonorably discharged. In 2003, when four Red Cross officials revealed that their group shipped blood tainted with AIDS, hepatitis and malaria viruses to hospitals, the Red Cross reprimanded them for “disorderly behavior.”

In 2005, a teacher was fired after exposing fellow school officials who raped deaf and mentally disabled students. He won his job back after a long legal battle.

In 2008, because of whistle-blowing by Kim Yong-chul, a former legal counsel of Samsung, South Korea’s largest conglomerate, investigators uncovered 4.5 trillion won ($4 billion) that its chairman, Lee Kun-hee, kept hidden under his aides’ names, and convicted him of tax evasion. Samsung vilified Mr. Kim as an untrustworthy former employee. Mr. Kim later wrote a book about the company.

When Lee Hae-gwan blew the whistle on the Jeju Island situation in early 2012, he was taking on a popular cause. At the time, he was a midlevel marketing staff member at KT Corporation, South Korea’s largest telecom company.

Kim Yoon-ok, South Korea’s first lady, was appointed as honorary chairwoman for a national committee supporting Jeju’s bid. The National Assembly adopted a unanimous resolution supporting the effort. Local campaigners encouraged people to vote as many times as they could, offering them free Hyundai and Kia cars via a lottery. Citizens, including children with their piggy banks, donated $5 million to help finance the telephone voting.

It worked: The poll sponsor, a Swiss foundation called New7Wonders, named Jeju Island one of the new seven wonders of nature.

But Mr. Lee and other workers wondered how KT’s lines could handle that volume of international calls, as well as how the fees from the phone calls might be divided between the phone company and New7Wonders. “It was not a vote, but rather more like buying a title with money,” Mr. Lee said.

In early 2012, he shared his misgivings with a local TV station and a government anticorruption commission. Authorities later fined KT less than $3,200, but the company also donated $4.1 million to help Jeju Island pay its phone bill.

Eamonn Fitzgerald, spokesman for New7Wonders, said his group took “a small portion” of the telephone fee paid by each voter and collected fees from corporate sponsors in the places competing for the title. Mr. Fitzgerald declined to say how many votes Jeju ultimately received, and the Jeju government declined to comment.

The furor died, but Mr. Lee began to feel rising pressure from his employer. First KT suspended him for two months. It then transferred him out of Seoul, forcing him to spend five and a half hours a day on the road. In his new post, he was shunned by colleagues and given maintenance duties that involved climbing telephone polls.

In late 2012, KT fired him, citing factors like taking sick leave without permission.

In February, South Korea’s top court affirmed an earlier decision that Mr. Lee’s punishments were a pretext and that he should be reinstated.

But KT was not done with him.

In March, he was punished with a month’s pay cut for the same reasons it had fired him in 2012. In a statement, KT said its action was justified and was not a reprisal for whistle-blowing. It has since rescinded the pay cut without explanation.

Mr. Lee cited what many workers in South Korea call “the bitter taste of organization.” “I blew the whistle expecting KT to apologize, fix the problem and move on,” he says. “How naïve I was.”