Mr Donal Spring, a solicitor and brother of the former Tanaiste, Mr Dick Spring, represented a foreign investor who secured an Irish passport in return for putting £1 million into a Tralee clothing company. He also acted for the company, Kerry Classics, which received the investment. The application was one of three approved by cabinet shortly before the general election.
Kerry Classics, which produces fashion knitwear for the domestic and foreign market, received the investment after the rainbow government reversed its passports-for-sale policy last May.
Similar investments were also received by two other clothing firms, Rowear in Ballina, Co Mayo, and J.A. Hickey & Co in Dublin and Athy, Co Kildare.
Mr Donal Spring is an expert in immigration law and is understood to have handled a small number of other passports-for-investment cases in the past three years.
His brother, the Labour Party leader, yesterday strongly defended the decision to process naturalisation certificates since it meant 200 jobs would be saved in Tralee, which is situated in his Kerry North constituency.
The managing director of Kerry Classics, Mr John Garrett, said: "Without the investment, this business would be closed".
The former government chief whip, Mr Jim Higgins, in whose constituency Rowear is situated, also defended the decision, shortly before the general election, that investors should be permitted Irish passports in return for putting money into the ailing firm.
Two Russians, Mr Nicholas Pochinkov and Mr Viatcheslav Bolotnikov, invested in J.A. Hickey & Co where about 300 jobs are understood to have been saved in producing women's clothes.
Politicians on all sides of the Dail, including the Taoiseach, Mr Ahern, as then leader of the opposition, are understood to have lobbied on behalf of the troubled companies.
The Fine Gael TD for Dublin Central, Mr Jim Mitchell, said that strong representations were "put repeatedly" by TDs from all parties in an attempt to save the company where 45 jobs were in jeopardy in Athy and more than 200 more at Inchicore, Dublin.
However, Mr Mitchell said that, although he had lobbied on the company's behalf, he did not agree with the scheme and would prefer to see a State agency such as Foir Teoranta dealing with companies in difficulty.
Meanwhile, it has emerged that the former minister for justice, Mrs Nora Owen, processed 44 passports during her time in office. A total of 29 applications had been "hanging over" since the time of her predecessor, Mrs Maire Geoghegan-Quinn, but only a dozen of these were finalised by Mrs Owen.
The Department of Justice provides "naturalisation certificates" for non-nationals, and this documentation is a prerequisite for obtaining an Irish passport.
The rainbow government decided in September 1996, and again in March this year, that applications for naturalisation should not be proceeded with until the scheme had been put on a statutory footing. However, a fortnight before polling day, the cabinet overturned its own policy and sanctioned three naturalisation certificates in return for investment in the clothing companies.
According to sources, the fact that the firms faced closure was the reason behind the decision.