In a nutshell, they aren’t taking either side but are offering a third side, that is “that of the full spectrum of today’s professional authors. Simply put, neither Amazon.com nor Hachette Book Group would exist without the work of professional authors.” In other words, they want the two sides to resolve this issue fast as it’s hurting author’s incomes.
By the way, the TWUC’s official position is that 25% royalties on e-book sales is far too low and “does not reflect a marketplace reality”, indicating that 50% would be more realistic. I don’t disagree with them, but I doubt this will happen anytime soon either. You can read what else they say at http://www.writersunion.ca/news/public-statement-amazoncom-hachette-book-group-dispute