Is cajun an ethnicity?

I am proud to say that I am of Cajun ancestry. My father’s family comes from a small area in southeast Louisiana that was founded by a small group of people with their own language, customs, etc. Unfortunately when he grew up (he is in his 60s) cajuns were discriminated against so he was not taught to speak cajun nor could he say he was cajun. I am always seeing on applications a section for race and/or ethnicity. Well, I have learned cajun. I was taught by my grandfather as a child and am proud of the culture. I therefore claim cajun to be my ethnicity in the same way someone would say they are hispanic. As far as race, I am caucasian. I am bringing this up because I was corrected today on an application by another race. For my race I put caucasian but for ethnicity, cajun. I was rudely told that I cannot put cajun I would have to put caucasian for both. Why? As far as I understand the definition, I should be able to claim cajun as my ethnicity.
To honey, cajun is a style of food derived from the cajun people’s lifestyle. Cajun people do have there own language, cajun. the cajun language is based off of french but is entirely different in pronunciation as well as some vocabulary differences. Most French people cannot understand Cajuns. Also, cajun and creole is totally different. I am cajun not creole.

Cajun is most certainly an ethnic group. I found this in Wikipedia:
"…Ethnic group of national origin….
The Cajuns retain a unique dialect of the French language and numerous other cultural traits that distinguish them as an ETHNIC group. Cajuns were officially recognized by the U.S. government as a national ethnic group in 1980 per a discrimination lawsuit filed in federal district court. Presided over by Judge Edwin Hunter, the case, known as Roach v. Dresser Industries Valve and Instrument Division (494 F.Supp. 215, D.C. La., 1980), hinged on the issue of the Cajuns’ ethnicity. Significantly, Judge Hunter held in his ruling that:

"We conclude that plaintiff is protected by Title VII’s ban on national origin discrimination. The Louisiana Acadian (Cajun) is alive and well. He is “up front” and “main stream.” He is not asking for any special treatment. By affording coverage under the “national origin” clause of Title VII he is afforded no special privilege. He is given only the same protection as those with English, Spanish, French, Iranian, Portuguese, Mexican, Italian, Irish, et al., ancestors." …."