Samsung phones. Hyundai cars. LG TVs. South Korean exports are available in virtually every corner of the world. But the nation is more dependent than ever before on an import to keep its factories and farms humming: foreign labor.

This shift is part of the fallout from a demographic crisis that has left South Korea with a shrinking and aging population. Data released this week showed that last year the country broke its own record — again — for the world’s lowest total fertility rate.

President Yoon Suk Yeol’s government has responded by more than doubling the quota for low-skilled workers from less-developed nations including Vietnam, Cambodia, Nepal, the Philippines and Bangladesh. Hundreds of thousands of them now toil in South Korea, typically in small factories, or on remote farms or fishing boats — jobs that locals consider too dirty, dangerous or low-paying. With little say in choosing or changing employers, many foreign workers endure predatory bosses, inhumane housing, discrimination and other abuses.

One of these is Chandra Das Hari Narayan, a native of Bangladesh. Last July, working in a wooded park north of Seoul, he was ordered to cut down a tall tree. Though the law requires a safety helmet when doing such work, he was not given one. A falling branch hit his head, knocking him out and sending blood spilling from his nose and mouth.

After his bosses refused to call an ambulance, ​a fellow ​migrant worker ​rushed him to a hospital, where​ doctors found internal bleeding in his head and his skull fractured in three places. His employer reported only minor bruises to the authorities, according to a document it filed for workers’ compensation for Mr. Chandra without his approval.

“They would not have treated me like this if I were South Korean,” said Mr. Chandra, 38. “They treat migrant workers ​like disposable items.”

The work can be deadly — foreign workers were nearly three times more likely to die in work-related accidents compared with the national average, according to a recent study. Such findings have alarmed rights groups and foreign governments; in January the Philippines prohibited its citizens from taking seasonal jobs in South Korea.

But South Korea remains an attractive destination, with more than 300,000 low-skilled workers here on temporary work visas. (Those figures do not include the tens of thousands of ethnic Korean migrants from China and former Soviet republics, who typically face less discrimination.) About 430,000 additional people have overstayed their visas and are working illegally, according to government data.

Migrant workers often land in places like Pocheon, a town northeast of Seoul where factories and greenhouses rely heavily on overseas labor. Sammer Chhetri, 30, got here in 2022 and sends $1,500 of his $1,750 monthly paycheck to his family in Nepal.

“You can’t make this kind of money ​in Nepal,” said Mr. Chhetri, who works from sunrise to dark in long, tunnel-shaped plastic greenhouses.

Another Nepalese worker, Hari Shrestha, 33, said his earnings from a South Korean furniture factory have helped his family build a house in Nepal.

Then there is the allure of South Korean pop culture, its globally popular TV dramas and music.

“Whenever I call my teenage daughter back home, she always asks, ‘Daddy, have you met BTS yet?’” ​said Asis Kumar Das, 48, who is from Bangladesh.

For nearly three years, Mr. Asis worked 12-hour shifts, six days a week, in a small textile factory for a monthly salary of about $2,350 — which he did not regularly receive.

“They have never paid me on time or in full,” ​he said​, showing an agreement his former employer signed with him promising to pay part of his overdue wages by the end of this month.

Mr. Asis is far from alone. Migrant workers ​annually report $91 million in ​unpaid wages, according to government data.

The Labor Ministry said it is “making all-out efforts” to improve working and living conditions for these workers. It is sending inspectors to more workplaces, hiring more translators and enforcing penalties for employers who mistreat workers, it said. Some towns are building public dormitories after local farmers complained that the government was importing foreign workers without adequate housing plans.

The government has also offered “exemplary” workers visas that allow them to bring over their families. Officials have said that South Korea intends to “bring in only those foreigners essential to our society​” and “strengthening the crackdown on those illegally staying here.”

But the authorities — who plan to issue a record 165,000 temporary work visas this year — have also scaled back some services, for instance cutting off funding for nine migrant support centers.

In the decades after the Korean War, South Korea exported construction workers to the Middle East and nurses and miners to Germany. By the early 1990s, as it emerged as an economic powerhouse churning out electronics and cars, it began importing foreign workers to fill jobs shunned by its increasingly rich local work force. But these migrants, classified as “industrial trainees,” were not protected by labor laws despite their harsh working conditions.

The government introduced the Employment Permit System, or E.P.S., in 2004, eliminating middlemen and becoming the sole job broker for low-skilled migrant workers. It recruits workers on three-year visas from 16 nations, and in 2015 also started offering seasonal employment to foreigners.

But severe issues persist.

“The biggest problem with E.P.S. is that it has created a master-servant relationship between employers and foreign workers,” said Kim Dal-sung, a Methodist pastor who runs the Pocheon Migrant Worker Center.

That can mean inhumane conditions. The “housing” promised to Mr. Chhetri, the agriculture worker, turned out to be ​a used shipping container hidden inside a tattered greenhouse-like structure covered with black plastic shading.

During a bitter cold snap in December 2020, Nuon Sokkheng, a Cambodian migrant, died in a heatless shack. The government instituted new safety regulations, but in Pocheon many workers continue to live in substandard facilities.

If E.P.S. workers have abusive employers, they often have only two choices: endure the ordeal, hoping that their boss will help them extend or renew their visa, or work illegally for someone else and live in constant fear of immigration raids, the Rev. Kim said.

In December 2022, Ray Sree Pallab Kumar, 32, lost most of the vision in his right eye after a metal piece thrown by his manager bounced off a steel-cutting machine and hit him. But his employers, in southern Seoul, sought to blame him for the accident, according to a Korean-language statement they tried to make him sign even though he didn’t understand it.

Migrants also say they face racist or xenophobic attitudes in South Korea.

“They treat people differently according to skin colors,” said Mr. Asis, the textile worker. “In the crowded bus, they would rather stand than take an empty seat next to me. I ask myself, ‘Do I smell?’”