I have heard of ALPA but I have never seen or heard them organize a distinct plan of forced action that will make an airline reconsider its terms if they want to keep operating.
Propeller pilot, unfortunately the 1Time pilot's need to collectively stand together and form a branch of Alpa - Sa. Then by all means Alpa - SA will effectively assist where they can. Until such time as that happens, Alpa has no jurisdiction or say in the treatment of 1 time pilots.
Have a look at the branches that form the Alpa union. SAAPA being the largest similiar to the union you mention in Germany, Cpa, Saxpa and Mango. So in essence without a voice the plight of the 1 Time guys will fall on deaf ears!