There is no evidence that J.P. Morgan treated his employees any worse than any of the other major financiers of the late 1800s and early 1900s. However, given the fact that management during that time period pushed as hard as they could with regard to working hours in a day while keeping wages as low as possible, and given that union protections that are commonplace today were not a part of the workingman's experience in the time period, working for Morgan's companies was a dreary prospect, just as working in any other factory would have been.
One example of the way that J.P. Morgan and other industrial barons treated their employees took place in 1900. Coal mining, then as now, was one of the most dangerous occupations available. At that time, workers were in near complete darkness, and the "black lung" killer (the accumulation of coal dust in the lungs) meant that few coal miners made it past the age of 50. In 1900, the average miner brought home about $400 a year, which was not enough for him to support his family, so his wife would have to bring in boarders to rent rooms, and his sons would have to quit school at the age of nine to work in a coal processing plant, picking out rock and slate with their fingers for a mere 45 cents a day. In 1900, miners in eastern Pennsylvania went on strike, and it was not until coal shortages were making their way across America that Morgan intervened with local mine owners to approve a 10 percent raise. Morgan was clearly in favor of letting the market determine wages until protest became too disorderly.