You can find the petition at:
We, the undersigned, wish to express our concern with the Joomla Core Team’s decision to force third party developers to reliance their extensions to the GPL.
The current mixture of GPL and commercial development has helped to grow Joomla to be the world’s leading Content Management System, for over 100,000 users. The new direction on strict GPL licensing threatens this ecosystem.
We therefore ask that the new GPL only policy is withdrawn, and that Joomla reinstates its previous policy to allow a mixture of GPL and commercial third party software.
If you share that viewpoint, you should head on over and leave you signature…