But the union has dismissed accusations it mis-sold top-up pensions and other products to members after a primary teacher in Livingston last week had a complaint against EIS Financial Services upheld by the pensions ombudsman. Some 9,000 teachers use the service.
Graham Dane, an Edinburgh secondary teacher who is campaigning to become union vice-president, this week questioned the link on the back of grass-roots concern about the lack of independent advice from the financial services arm. The EIS company only recommends products sold by Scottish Amicable, the Stirling-based company that three years ago merged with the Prudential.
Mr Dane said: "The EIS does not run businesses. It does not endorse travel agents, furniture companies or even educational resources. There is no good reason that I can see for the association to continue, unless it can be shown that there is a healthy inflow of funds to the EIS from the company.
"Even then it would only be justifiable if it could be shown that it did not disadvantage individual members."
When the unnamed Livingston teacher saw an EIS representative five years ago, she thought she was receiving impartial advice about additional voluntary contributions (AVCs) to top up her pension. EIS Financial Services' promotional material emphasises it is "a representative oly of the Scottish Amicable Marketing Group".
The teacher claimed she was sold the wrong type of pension, a view shared by the ombudsman who has ordered compensation of around pound;7,000. Scottish Amicable is now challenging the decision.
In a curious but unrelated twist, Jim Martin, the union's former general secretary, left to join Scottish Amicable five years ago, but has subsequently quit.
Ronnie Smith, the current general secretary, has now written to members emphasising that the judgment was a one-off. "Any idea there is a general issue here is not confirmed by the ombudsman's finding," Mr Smith told The TES Scotland. The tenth anniversary review of the link, initiated before the present furore, would consider future arrangments.
Lesley Collins, managing director of Edinburgh-based Teachers' Independent Financial Services, who once worked for EIS Financial Services, said: "To meet the clients' needs you have to look at the overall picture and that can only be provided by having full access to product ranges available in the market-place."
Before the link with Scottish Amicable, which insiders suggest is one of the better tie-ins, the union was involved in selling products from Commercial Union.
Top-up pensions through the Scottish Teachers' Superannuation Scheme are arranged, ironically, through the Prudential, which has been identified throughout the UK as the preferred company. But EIS Financial Services advisers can only recommend Scottish Amicable deals.