By Ju-min Park and Heejin Kim

SEOUL, Sept 12 (Reuters) - South Korea has ramped up

calls for changes to the U.S. visa system so that its workers

can visit for longer periods after an immigration raid at a

battery plant in Georgia led to the detainment of hundreds of

its citizens.

The two countries are looking at establishing a working

group to consider a new type of visa for Koreans, according to

South Korea's foreign minister who visited Washington this week.

WHAT HAS BEEN THE PROBLEM?

South Korean companies have become major investors in the

U.S., building factories that often require highly technical

skill sets that are not easy to find in the United States.

But unlike some countries such as Australia, Canada and

Mexico, South Koreans do not have access to special treaty work

visas.

"There's really no mid-term business visa for Korean

businessmen to work in the U.S. for several months," said Kim

Yong-sang, a Seoul-based lawyer specialising in international

disputes at Yulchon LLC

Instead, sources have said employees of South Korean

companies commonly use either the Electronic System for Travel

Authorization (ESTA), a type of visa waiver that allows for

stays of up to 90 days or B-1 visas - a temporary visa for some

business-related activities.

Both of these visas limit what work can be done in the

United States, which has meant that some South Korean workers

have been relying on grey areas in U.S. visa enforcement.

There's also been a "lack of coordination between federal

and state immigration policy," said Jihae Han, a U.S. attorney

at Maru Law Firm. "Many U.S. state and local officials are

unaware of how complex and serious the visa bottleneck is."

IS THE US WILLING TO CHANGE?

South Korea has pushed for years for a bill that would

create or expand visa categories to accommodate skilled South

Korean nationals who need to visit the United States for longer

periods.

That bill has had difficulty getting through Congress

because visas are linked to immigration, one of the most

sensitive subjects in the United States, according to South

Korea's foreign ministry.

U.S. immigration officials initially trumpeted the raid at

the Hyundai Motor ( HYMLF ) and LG Energy Solution

battery project site. But U.S. President Donald Trump's

administration has also signalled it recognises the importance

of South Korean investment and the skills of the country's

workers needed to get plants operational.

Trump earlier this week offered to allow the workers to stay

in the United States to train Americans.

The workers may return to the U.S after resting at home,

South Korea's foreign ministry said.

U.S. Commerce Secretary Howard Lutnick said on Thursday that

Hyundai should have called him to secure the right visas.

"I called up the Koreans, I said, oh, give me a break. Get

the right visa and if you're having problems getting the right

visa, call me," Axios quoted him as saying in an interview.