Can I be legally be fired for choosing to no longer speak spanish at work?

I've worked retail for 3years and I'm bilingual. I had no problem dealing with Spanish only customer service until they restructured our sales goals. Taking the time to do Spanish customer service takes me away from the floor and those who don't speak Spanish get to stay on the floor and get sales. I told my boss that this was unfair since I was loosing potential sales. He yelled at me and told me I was burning bridges and threatened to have me transferred because I didn't fit the team if I refused to speak Spanish. We do not get bilingual pay, and there are other employees who don't speak Spanish, so regardless if Spanish only sales do come in they are going to leave because there's not always someone on shift to help them. Can I legally be fired because I refuse to give in?