역제소 is a term used in the legal field. You will see it often in the newspaper and other publications. It’s not in the dictionary. However, it’s easier to determine the meaning by trying to get some additional context and looking at the overall meaning of the text.

Sometimes this is written as “역 제소” but it appears “역제소” without the space is the standard form of writing.

오히려 역 제소를 당하고 있는 실정입니다. 이대로 계속 진행을 하다 가는 반감은 반감대로 얻고, 이득은 챙기지 못할 공산이 큽니다

역제소 = counter-suit, [filing a] counter lawsuit

Here are some news sources for context:

http://www.hani.co.kr/arti/economy/economy_general/73532.html

https://biz.chosun.com/site/data/html_dir/2012/12/26/2012122600423.html

https://www.etnews.com/201204040041?m=1