The only sources that I have read that suggested there was any large scale slavery or indentured servitude involving the Chinese were fictional.
The Chinese laborers had a good rep from previous projects in Cal. They only worked the Pacific to east portion BTW, over the worst terrain, the Sierra Nevada. The project from the other direction had the then largely untamed Indian tribes to contend with and also exploited an immigrant group to help get it done. The Mormons recruited from back east and Europe for laborers, promising a homestead when they were finished as their reward. Many ended up not being paid by the church, but at least they had their way paid to America by the Mormons.
In Stephen E. Ambrose's book "Nothing Like It In The World," The Men Who Built The Transcontinental Railroad 1863-1869, he points out on p. 21 that:
"...That included the thousands of Chinese working for the Central Pacific. Contrary to myth, they were not brought over by the boatload to work for the railroad. Most of them were already in California. They were glad to get the work. Although they were physically small, their teamwork was so exemplary that they were able to accomplish feats we just stand astonished at today..."
There is a lot more information on the Chinese laborers' contribution to the building of the west end of the rail line in his book, the most difficult part. There were a lot of Chinese already here, but they were also recruited in China by overseas merchants touting the expensive labor in California.
pp. 151-152:
"...After 1858, many Chinese had come to America in response to pamphlets put out by several companies of Chinese merchants residing in San Francisco, advertising the high price of labor. The merchant companies took their pay from a percentage of a man's earnings, plus a large bonus. They agreed to return a man to China free of charge; in the event of sickness he would be cared for; in case of death they would send the body home to be buried in the Celestial Empire. These contracts were faithfully fulfilled. Nonetheless, the ships rivaled the slave ships for gruesomeness.
In California the Chinese could find work as domestic cooks, laundrymen, housekeepers, gardeners, errand boys, and so on. Like most previous immigrants, they sent back to China letters to their families, urging their wives, children, parents, brothers, and sisters to come. They landed in San Francisco, which had the largest number of Chinese and was known to them in their own language as "the big city - Tai Fau - first city." Next came Sacramento, the "Yi Fau," or the second city. Marysville was the third city..."
The real reason the Chinese ended up the marjority of the laborers on this west end of the construction was that initially the men that were hired were either gold diggers, that had arrived in SF with nothing, but took a job with the railroad and at the occasion of their first paycheck, bought tools and hightailed off the job to dig gold in them thar hills. Most of these men were unaware that the large surge of the actual gold rush from 1848-1860 was essentially over.
The other groups were ex-civil war soldiers and groups of immigrant labor such as the Irish. These groups also proved unreliable as they drank, fought, and generally were not manageable as a work force for such a demanding task. On the other hand after the initial doubts by some of the bigwigs building it like Strobridge and Crocker, the Chinese were found to perform superbly.
"...They worked as teams, took almost no breaks, learned how to blast away rocks, stayed healthy and on the job. Engineer Montague praised them and declared in his 1865 report, "The experiment has proved eminently successful." The CP began to hire them locally, offering $28 a month, then $30, then $31. Those were big wages even when the men had to pay for their own food. Crocker turned to a labor contractor in San Francisco, Koopmanschap, and had him look across the state for two thousand more "coolies," and even to import them from China if necessary. Before the end of 1865, there were seven thousand Chinese at work on the line, with just under two thousand whites."
Nothing Like It In The World, p. 152.
CHINESE-AMERICAN CONTRIBUTION TO TRANSCONTINENTAL RAILROAD
...Chinese labor was suggested, as they had already helped build the California Central Railroad, the railroad from Sacramento to Marysville and the San Jose Railway. Originally thought to be too small to complete such a momentous task, Charles Crocker of Central Pacific pointed out, "the Chinese made the Great Wall, didn't they?"
The first Chinese were hired in 1865
at approximately $28 per month to do the very dangerous work of blasting and laying ties over the treacherous terrain of the high Sierras. They lived in simply dwellings and cooked their own meals, often consisting of fish, dried oysters and fruit, mushrooms and seaweed.
Work in the beginning was slow and difficult. After the first 23 miles, Central Pacific faced the daunting task of laying tracks over terrain that rose 7,000 feet in 100 miles. To conquer the many sheer embankments, the Chinese workers used techniques they had learned in China to complete similar tasks. were lowered by ropes from the top of cliffs in baskets , and while suspended, they chipped away at the granite and planted explosives that were used to blast tunnels. Many workers risked their lives and perished in the harsh winters and dangerous conditions.
By the summer of 1868, 4,000 workers, two thirds of which were Chinese, had built the transcontinental railroad over the Sierras and into the interior plains. On May 10, 1869, the two railroads were to meet at Promontory, Utah in front of a cheering crowd and a band. A Chinese crew was chosen to lay the final ten miles of track, and it was completed in only twelve hours...
http://cprr.org/Museum/Chinese.html
I don't think there were anything like labor unions in the 1800s, so that theory is not valid in terms of the Chinese being hired to bust unions here.
That came later, like with Nixon and the recognition of China and Chinese opening the door to the outside world in the 1970s, making their workforce a player on the global stage.
Hands off my Social Security!
Hands off Latin America!
Just my dos centavos
robdogbucky