THE lead-up to the European Parliament elections tomorrow might seem like business as usual, but with a potentially serious clash looming between EU prime ministers and the new parliament, both the electorate and the Government face crucial choices.

Significant changes have occurred since 2009. First, the euro crisis has transformed the context in which the elections take place. Surveys show that Irish people's trust in the EU since the bailout is 23 percentage points lower than before the crisis and this has impacted the campaign.

Second, the Lisbon Treaty entered into force in late 2009, considerably increasing the power of the European Parliament and individual MEPs in the complex EU system. Since then, the parliament has significantly influenced a number of important decisions, including on the EU's seven-year budget and the Single Resolution Mechanism for the winding-up of troubled banks.

A third major change, which has thus far been invisible in the Irish campaign, is the impact of the results on the selection of the next European Commission President. Due to changes introduced by the Lisbon Treaty, this year's elections will have a bearing on how this powerful position is filled.

Exactly how the results will be translated into the choice of commission president is the subject of disagreement between those involved, stemming from differing readings of the Lisbon Treaty.

The European Parliament has moved to implement its interpretation, with the main political families – centre-right centre-left, liberal, green and left – each announcing a lead candidate for the position. They envisage that once the election results are known, the candidate of the largest group will succeed the outgoing president, Jose Manuel Barroso.

Some national leaders disagree with this interpretation, saying it ignores the role of the member states, which is also enshrined in the treaties (article 17.7 and declaration 11). Others, such as UK Prime Minister David Cameron, have stated that none of the lead candidates is acceptable. Thus, the stage is set for a clash between the European Parliament and the member states over the leadership of the commission.

Voters should be aware that their votes will, directly or indirectly, influence the selection of the commission president. A vote for Fine Gael will strengthen the case for a Christian Democrat president from the European People's Party, Jean-Claude Juncker, former prime minister of Luxembourg. A vote for the Labour Party will support the candidacy of a centre-left president from the Socialists and Democrats family, Martin Schulz.

Meanwhile, the Irish Government must decide on the approach it will advocate. Taoiseach Enda Kenny will represent Ireland at a European Council dinner on May 27, where national leaders will hold initial discussions on the options for commission president in light of the election results.

The Government may support the lead candidate of the group that wins the most seats. A major advantage is the increased likelihood of a smooth process, avoiding institutional stalemate. Leading MEPs have also suggested that this system would bring the institutions closer to citizens, enhancing democratic legitimacy. This is difficult to argue in the Irish case, however; an IPSOS poll found that less than 30pc of Irish voters surveyed were aware of or had an opinion on each of the lead candidates.

Alternatively, the Government could insist on the prerogative of the member states (through the European Council) in nominating the commission president. Arguments for this approach include balancing the roles of the parliament and the member states in the decision and tempering the politicisation of the commission, which risks irreversibly changing the nature of the institution that has traditionally safeguarded the interests of the smaller states. A positive side effect would also be to avoid marginalising the UK.

If the latter position prevails in the European Council, the outcome is unpredictable. Consultations and informal contacts between the institutions and the capitals will strive to find a compromise candidate. In this scenario, the votes of citizens in the European Parliament elections would feed into the decision by determining the political persuasion of the nominee.

The European election tomorrow cannot be seen as business as usual. The Government faces a strategic decision on how to expend its political capital in the wake of the elections. Voters must weigh up their preferences on a range of issues, including who should be the next commission president.

Linda Barry is a senior researcher at the Institute of International and European Affairs

Irish Independent