What action are you thinking of which isn't done? In the Bundestag, they can't do more than argue and vote against (which they do). In the Bundesrat, they have more clout. In particular the SPD via Grand Coalition governments like Thuringia's, where I'm reading that the SPD minister is using strong words. (Based on the same article, I must correct myself however; the feed-in law reform doesn't need to pass the Bundesrat, they can only blackmail by blocking another law.) There is a possibility of attacking the law before the constitutional court, but that comes only after it took effect. That leaves street protests, I guess? Currently the homepage of the Greens is headlined by a call to participate in the protest on 5 March, with a link to the solar industry association's page on it.

_{*Lunatic*, n.
One whose delusions are out of fashion.}