AMBON, INDONESIA

Tens of thousands of invisible migrants stream into Thailand, Southeast Asia’s second-largest economy, every year. Many are used as forced labor in various industries, especially on long-haul fishing boats that catch seafood eaten in the U.S. and around the world. Others are dragged into the country’s booming sex industry. Ethnic Rohingya asylum seekers from neighboring Myanmar are also held for ransom in abysmal jungle camps.

Next week, when a U.S. report on human trafficking comes out, Thailand may be punished for allowing that exploitation. The country has been on a U.S. State Department human trafficking watch list for the past four years. Washington warned in last year’s report that without major improvements, it would be dropped to the lowest rung, Tier 3, joining the ranks of North Korea, Syria, Iran and Zimbabwe.

Though Thailand says it is trying to prevent such abuses and punish traffickers, its authorities have been part of the problem. The U.S. has said the involvement of corrupt officials appears to be widespread, from protecting brothels and workplaces to cooperating directly with traffickers.

A downgrade could lead the U.S. to pull back certain forms of foreign support and exchange programs as well as oppose assistance from international financial institutions such as the World Bank. Washington has already cut some assistance to Bangkok following last month’s Thai military coup.

Thailand is paying a U.S. public relations company $51,000 a month to help in its push for better standing. The government issued a progress report for 2013, noting that investigations, prosecutions and the budget for anti-trafficking work all are on the rise.

“We recognize that it’s a very serious, very significant problem, and we’ve been building a legal and bureaucratic framework to try to address these issues,” said Vijavat Isarabhakdi, Thailand’s ambassador to the U.S. “We feel that we have turned a corner and are making great progress in this area.”

At least 38 Thai police were punished last year or are being investigated for involvement in trafficking, but none has stood trial yet. Four companies have been fined, and criminal charges against five others are pending. But the government pulled the licenses of only two of the country’s numerous labor recruitment agencies.

In Geneva on Wednesday, Thailand was the only government in the world to vote against a new U.N. international treaty that combats forced labor by, among other things, strengthening victims’ access to compensation. Several countries abstained.

“Thailand tries to portray itself as the victim while, at the same time, it’s busy taking advantage of everybody it can who’s coming through the country,” said Phil Robertson, deputy director of Human Rights Watch’s Asia division. “The exploitation of migrants, the trafficking, it comes through Thailand because people know they can pay people in the government and in the police to look the other way.”

Thailand shipped some $7 billion worth of seafood abroad last year, making it the world’s third-largest exporter. Most went to Japan and the U.S., where it ranks as the No. 3 foreign supplier.

The United Nations estimates the industry employs 2 million people, but it still faces a massive worker shortage. Many Thais are unwilling to take the lowpaid, dangerous jobs that can require fishermen to be at sea for months or even years at a time.

An estimated 200,000 migrants, mostly from neighboring Myanmar and Cambodia, are laboring on Thai boats, according to the Bangkok-based nonprofit Raks Thai Foundation. Some go voluntarily, but a U.N. survey last year of nearly 600 workers in the fishing industry found that almost none had a signed contract, and about 40 percent had wages cut without explanation. Children were also found on board.

Forced or coerced work is more common in certain sectors, including deep-sea fishing and seafood processing plants where some workers have reported being drugged and kidnapped.

The problem is also rampant in the country’s notorious sex industry. More than three-quarters of trafficking investigations launched last year in Thailand involved sexual exploitation. Thai girls and women were abused along with those from neighboring countries.

Another challenge surrounds the recent influx of Rohingya Muslims. An estimated 75,000 have fled Myanmar since communal violence exploded there two years ago, according to Chris Lewa of the nonprofit Arakan Project. The Buddhist dominated country considers Rohingya to be noncitizens from Bangladesh, though many were born in Myanmar.

Many Rohingya brought to Thailand are held at rubber plantations or forest camps by armed guards until they can find a way to pay the typical asking price of $2,000 for their release, according to victims and rights groups. Those who get the money often cross the border into Malaysia, where tens of thousands of Rohingya have found refuge. Those who don’t are sometimes sold for sex, forced labor, or they are simply left to die.

The Thai government, however, does not address these asylum seekers as trafficking victims in its report. It said fleeing Rohingya enter Thailand willingly, even though “most of them fall prey to smugglers and illegal middlemen.” However, Vijavat, the Thai ambassador, said some cases are now being treated as trafficking.

Rights groups allege corrupt Thai officials are sometimes involved, including deporting Rohingya straight back into traffickers’ hands.