The government is having to defend its decision to pay additional money into the pension funds of post-1994 MPs on affirmative action grounds.
If it loses the court case, Trevor Manuel's finance ministry could be forced to pay out R30-million to MPs who served in parliament before the African National Congress came into power.
The government has already lost the first round, and Manuel has lodged an appeal with the Constitutional Court. The appeal will be heard on Tuesday.
The case was brought by 167 disgruntled MPs led by former National Party MP Frik van Heerden, who have waged a protracted legal battle in which they have had to overcome several technical defences.
In their lawsuit, the group of MPs named Manuel, who took over as head of the ministry in 1997, Speaker of parliament Frene Ginwala and the Political Office-Bearers Pension Fund.
Their claim was based on a policy that allowed the state to contribute more money to the pensions of new MPs.
The group won the first round when the Cape High Court ruled that pension measures applied by ministers of finance between 1994 and 1999 were indeed unfair and unconstitutional.
The ministry's legal team had stated in papers before court that the policy was "limited affirmative action" and justified as the majority of new MPs had been excluded from parliament because of their race and their membership of (banned) political parties.
In his judgment, Mr Justice Wilfred Thring ruled in favour of Van Heerden and his co-litigants.
He said the differentiation in pension fund contributions was arbitrary, unfair, unreasonable and discriminatory. The policy, he added, discriminated against members of the old regime's parliament in a way that was not allowed by the constitution.