In a case taken by Dublin West constituent Feargal Molloy, the High Court will be asked to declare that Environment minister Dick Roche has the legal power to turn Dublin West into a four-seat constituency before polling day. Dublin West currently has a population-to-TD ratio of 31,000:1, leaving it clearly under-represented under the constitution's strict guidelines.

A section of the 1992 Electoral Act gives the minister the power to fix any problem in relation to the election by ministerial order . . . including a change to the 2005 Electoral Amendment Act underpinning the current constituencies.

The ministerial order is valid once made. The state is likely to argue in court that it would be unconstitutional for a minister, rather than the Oireachtas, to change an act. However, the High Court has already found, in an earlier case, that the minister has powers to amend the Electoral Act using this section.

The High Court cannot compel the minister to add an extra TD in Dublin West, but if it rules that he has the power to do so, it may put the government in an awkward position.

Any increase in the number of TDs for Dublin West, which would raise the number of TDs in the next Dail to 167, would likely benefit the alternative Rainbow, guaranteeing it two seats there.

Molloy's case will be heard on Tuesday, at the same time as a constitutional challenge, by independent TDs Catherine Murphy and Finian McGrath, against the current constituencies.