The European Commission on Thursday invited public comment on P&O Stena Line's request to extend its exemption from competition rules on ferry runs between Britain and mainland Europe. The Commission said it was "inviting interested parties to submit their comments within 30 days" on renewing the joint venture's three-year exemption from rules that often bar competitors from teaming up together. The exemption expires on March 10. The Commission said no official complaint had been received about competitive effects of the joint venture over the past three years, although some consumers took a different view. "The Commission will carefully consider the various letters it has received from individual consumers complaining of increased prices for their cross-Channel travel…