Willie Nelson performing at the 'Hard Rock's 2007 Ambassadors of Rock Tour' event held at the Hard Rock Cafe, New York City, USA - 10.09.07

Nelson and the Animal Legal Defense Fund (ALDF) are trying to organise a boycott of milk produced at California's Mendes Calf Ranch, where activists claim calves are being raised in cramped and dirty crates.

The ALDF is currently preparing a lawsuit against the Mendes Ranch.

The singer has written a letter to a number of companies and is urging people to add their names to the 22,000 strong petition.

Source: WENN