The notice is here, signers include Bob Solow and Dani Rodrik. I agree with their arguments, and you will find my slightly different but still consistent earlier critique here. Here is one bit from the press release:
“It’s a widely shared opinion among economists that the court’s attempt to force Argentina into a default that nobody – not the debtor nor more than 90 percent of creditors – wants, is wrong and damaging,” said Mark Weisbrot, economist and Co-Director of the Center for Economic and Policy Research, who helped circulate the letter.
Matt Levine has a good post on the situation here.