Can a company fire US citizen after they find cheap foreign worker without any work auth?

I am US citizen. I was employed as technology consultant initially for 3 months contract. During the middle of the contract they liked my work and told me they would extend my contract to 2 more months. But all this changed once they found remote indian programmers working from india (without any visa to work in usa)for much lower rate. My hourly is comparable to previling market rate for a US citizen. They told me i am the most expensive resource and suddenly terminated my contract without advance notice. Is this legal? Do I have a good legal case? I believe this is clear violation of US labor laws. The company is US company located in Colorado and its a publishing company and I was involved with IT division of the company also located in Colorado. All the managers I worked with during the project are located in Colorado.