As of 1 April 2018, all textiles made of organic cotton or with organic cotton parts are tested for genetically modified organisms (GMO) within the scope of product certification as per STANDARD 100 by OEKO-TEX®. 

The additional laboratory test is mandatory if the applicant company wishes to label articles on the STANDARD 100 by OEKO-TEX® certificate with the corresponding quality descriptions such as "organic".
More information on GMO testing of organic cotton
Frequently asked questions on GMO test for organic cotton