Pirc, the pensions and investments research consultants, said yesterday that it would make a formal complaint about the appointment at Next's annual meeting in May.
Pirc spokeswoman Anne Simpson said: "By and large we think there is a real problem having relatives on the board. These are public companies, not private dynasties. You have to ask what this tells you about the company's nominations procedure.
"If we think there is a case to answer regarding nepotism then we will advise our clients to vote against it."
Pirc's comments follow others made by Next's institutional investors after the retail group's announcement on Tuesday that the 29-year-old Mr Wolfson was to join the board. Next chief executive David Jones again defended the appointment yesterday: "As far as I am concerned I am not going to risk my reputation or shareholder value by making a wrong appointment.
"If they [Pirc] want to ask me anything I would be happy to meet them and answer them. I have absolutely no hang-up about this."
Mr Jones said it was he, not Lord Wolfson, who nominated Simon Wolfson and that his appointment was approved by the entire board. He said Mr Wolfson had been introduced to Next's leading shareholders and City analysts and had met with their approval.
Ms Simpson said the elevation of family members to the board of a public company was often not just a problem for the business but for the individual.
"If they are a non-executive there is a question over independence. If they are executive it can be difficult when they have daddy or mummy lurking about," she said.