Union leaders are hesitant to show their support for the Green New Deal while details of the legislation are still being drawn out. Once finalized, the Green New Deal would catalyze government-led investments in clean energy infrastructure and create jobs for Americans. Unions are taking issue with the current language, which asks workers to “just transition,” and union representatives want a clear and defined meaning on what that entails, as it could very well imply job losses in the near future.
See "Labor unions fear Democrats’ Green New Deal poses job threat", Valerie Volcovici, Reuters, February 12, 2019