In the early 1990s he was also a founding member of the Petition of Fifty, a movement for democratic reform which included conservative military figures who had fallen out with Suharto and which for the first time in decades raised a real challenge to his rule. Along with other members of the group including Ali Sadikin and Hoegeng, Princen again found himself persona non-grata with the regime, although he joked to his visitors that by that time he was "too old to put in jail again".