A charter bus crashed north of Little Rock, Arkansas, early Friday morning, killing six migrant workers and injuring several more. It was reportedly carrying the workers from Monroe, Michigan to Laredo, Texas.

The bus, which was carrying 22 people, crashed into the abutment of a highway overpass along Interstate 40 in North Little Rock at about 1 a.m. on Friday. Three of the dead were thrown from the bus, while three other bodies were found on board, according to Arkansas State Police Major Mike Foster.

Six others were treated for injuries at area hospitals. Media photographs show severe damage to the bus, particularly to its rear third, where the roof and side window were torn off by the impact.

The bus had been sold for $8,000 on Saturday from the Detroit-based Continental Charter bus service, to a private Florida company called Vasquez Citrus Hauling. Jeff Lawson, the owner of Continental, told the Arkansas Democrat-Gazette that the purchaser of the bus told him “he needed a second bus to haul people from (Detroit) to Texas... and Florida.” An advertisement for the firm posted earlier in the year sought agricultural workers in Michigan with terms of service ending in November.

The driver of the bus has been identified as Roberto Vasquez, 28, of Monroe, Michigan. Vasquez was not injured. Two other employees of Vasquez Citrus Hauling were also uninjured. The identities of the dead and injured among the migrant workers have not been made public.

“Reaching out to the families has been difficult but we’re receiving help from the Mexican consulate,” Foster said.

The Red Cross has provided temporary food and shelter to the survivors, who reportedly speak little English. Immigration and Customs Enforcement officers have been called into assist with communication. ICE spokesman Bryan Cox said the agency was not yet investigating the employers or passengers.

The cause of the single-vehicle accident is not clear. Storms had passed through the region on Thursday, but only mist and light rain were present at the time of the crash. The nature of the crash suggests that the driver might have fallen asleep. A spokesman for the National Transportation Safety Board, which will conduct an investigation into the crash, will focus on driver fatigue and passenger safety.

The crash in Arkansas underscores the highly exploitative nature of farm labor in the US, which is heavily dependent on undocumented and itinerant immigrant workers.

There are currently about one million hired farm laborers in the US, less than 1 percent of the overall US workforce. Of these, roughly one third are agricultural service workers brought to farms by labor contractors. According to data from the U.S. Department of Labor’s National Agricultural Workers Survey, about half of hired crop farmworkers are not legally authorized to work in the US. About two-thirds of these are Mexican nationals.

With labor costs accounting for an exceptionally high share of the cost of production for crops such as fruits, vegetables, and nursery products, these undocumented workers are vulnerable to extreme exploitation by farm owners and labor contractors. In 2011, farmworkers and laborers in these three agricultural industries had average annual earnings of just $20,000, according to the US Department of Agriculture’s Farm Labor Survey.

The several hundred thousand undocumented agricultural laborers in the US comprise a small share of America’s roughly 11 million undocumented immigrants, a critical section of the working class.