The problem today are the L-1 visas, which are relatively unregulated. L-1 visas are for foreign nationals in a management capacity whose companies wish to transfer them to the US. These visas only require that the employer pay the employee's living expenses, and the employee receives the normal salary they would make in their home country (!).
All of this is fine until you start to stretch the definition of "management". Which many consulting companies (Tata, Infosys, Cognizant, etc) have started to do -- they can take a person from India who is paid ~$25,000/yr (a good engineer's salary in India), fly him to the US on an L-1 visa, and charge him out to the client at $100/hr. An equivalent US-based contractor rate for the same position would be $125/hr and have margins around 10-15%. But the offshoring firms can undercut US-based contractors by 25%, eat all the travel/housing expenses, and STILL make well over 100% margins.
L-1s are actually the problem. There's no salary parity requirement, there's no requirement to look for US-based candidates of equivalent positions, just a requirement that the person is "acting in a management capacity" and has worked for the company for at least 1 year. It's hard to prove that someone is not "acting in a management capacity" -- many of the companies outright lie on the visa applications. What's worse, this type of dishonesty is considered fair game when dealing with corrupt bureaucracies in India or China. But L-1s are fueling the latest wave of offshoring: they allow companies to bring people to the US at offshore prices.