My job told me I have to stop flying business class for work. I'm a 5'2 120 pound woman. How can I argue this effectively?

I'm one of the only women in my IT department and travel for work every week. I'm 5'2 and 120. <br><br>I've been told I am only allowed economy from now on, even though I was told I could fly business class when I was hired. I feel like this is discriminatory and I am going to be uncomfortable in economy. What should I do?