I first heard about it here:
(scroll down to the third feature)
Here's some recent BF discussion:
Astana out of the Tour?
TDF a Threat to Cycling's Future
Whether Astana has changed enough from last year or not, Tour of California organizer AEG has actually set a better example for ASO. AEG blocked specific riders, not a whole team (see the first feature in that same cyclingnews link). Leipheimer is clean. Not even ASO has disputed that. Think he should contend le Tour? Like grassroots efforts?
Well then tell ASO yourself by signing your e-mail address to Levi's petition.
Please do not make this into a chain letter. Thank you for your support.