I worked with Kforce for a year placed on a client's location. As long as the contract continued, I had a great time. I was informed that my employment would end the last day of my contract, and I wouldn't be paid for this time. Typically, companies would give at least a few weeks after your contract got over before they terminate your employment.
They try to give ultimatums to people on Visas. I experienced it and also heard from my friends who worked there. I worked with them for more than a year and did my best work there. At the end of my current contract, they led me to believe that they were fervently seeking opportunities for me. I was told that they couldn't find any project for me and nothing was open all over the US. I have multiple certifications in relevant technologies that are always in demand. But, I was told that they could locate just one project for me and that was it. And, this position was in a place far away from my current location, and I'd have to take a pay cut. Because I'm on my visa, I wouldn't have much of a choice. I've heard similar horror stories from my fellow legal immigrants who are here on a Visa. One of my friends was offered a position in a major city where he'd take a 15% pay cut.
Just because a company is the employer and hold's an immigrant's visa, doesn't mean that they have the right to ill treat the person.