Roughly 80% of the refugees — 314 to be exact — are women. The refugees, arrested by Thai police over the last three months, face almost certain death if sent back to North Korea. They are demanding that they be allowed to travel to South Korea.  An NGO representative accuses South Korea of failing to help them:

However, “For whatever the reason, the South Korean government is not bringing these refugees who have been waiting for release even though the procedures have been finalized and the airplane tickets have been obtained” the affiliate said and added that there were even rumors to suggest that the refugees at the immigration centre would be denied the tickets altogether.  [Daily NK]

South Korea’s Foreign Minister denies that:

Regarding the hunger strike by the 400 defectors, Minister Song Min Soon of the Ministry of Foreign Affairs said, “We are aware that such an issue has arisen,” and “We are making efforts to come to some sort of agreement with Thai authorities in order to solve the matter.”  [Daily NK]

Yonhap adds some statistical context:

Activists claim that 622 North Korean defectors were arrested since 2003 at the checkpoint of Mae Sai in northern Thailand. Of those, 367 entered the country illegally last year.  [Yonhap]

Conditions in the Thai jail are said to be severely overcrowded and unsanitary, although they’re no doubt much better than they would be in China or North Korea.  The hunger strike puts South Korea in a difficult position.  They can either allow the 400 to be sent back to Kim Jong Il’s concentration camps — which would be especially hard to do in an election year — or they can allow another mass airlift such as the one from Viet Nam in 2004, which caused the North Koreans to have another of their contrived tantrums.
More info when I have it.