From a more sociological perspective, the San Antonio Express news agrees that requiring New Mexico employees to only speak English is wrong on many levels. See story. The Express news adds that New Mexico, of course, was Hispanic long before it became part of the US. According to the author, Ruben Navarrette, the employees who were fired come from old New Mexico families. So, they are no immigrants and are speaking their "normal" tongue.
As I recently posted, an employer who requires employees to only speak English must have a clear business reason. Otherwise, it will appear that discrimination was a motivating factor. The employer said he wanted employees to speak English because he was afraid they were talking about him in Spanish. Sigh.
The scary thing is the employer lived for many years in Texas and ran businesses here.