Dozens of workers lose their jobs for participating in Day Without Immigrants protest

If you just don't show up without some sort of call in or what ever the policy your work has then yes you are subject to termination.

Actions do not come without consequences.

Willing to bet there is more to the story (there always is). The company I worked for had a rolling 90 day attendance point system. Hate to tell you how many times I fired someone for exceeding the mandatory termination points of the policy. Probably half the time the person being terminated had a reasonable explanation for the absence that put him/her over the point limit. However I always had to remind them of the other times they earned points that led to the termination.
Also, many people fail to realize that many jobs are at the will of the employer. If this is the case people can be fired for any reason, period.