A clause in the SEC's proposed overhaul of Regulation AB is suddenly causing alarm among asset-backed bond issuers, who say the measure could kill the appeal of shelf entities. The main cause for concern: For an issuer to conduct a shelf offering, a top executive would have to sign statements essentially assuring bondholders that payments will be made in full and on time. Bank of America, J.P. Morgan, Wells Fargo and other issuers have submitted comments to the SEC strongly opposing the requirement.