LONDON, England (CNN) -- European Union members will learn Friday afternoon whether Irish voters have shot down or supported their latest attempt to create a new governing treaty.

Irish Prime Minister Brian Cowan and his wife Mary vote on the European Union treaty.
All EU member nations must approve the treaty for it to take effect, and Ireland is the only country to put the treaty to a popular vote. In other countries, legislators make the decision.
A "no" vote on the referendum would deal a significant setback to the 27-member EU. Opinion polls in Ireland have shown the vote is too close to call.
While the four main political parties support the document, a range of groups -- from farmers to business groups to some Catholic groups -- staunchly oppose it.
That opposition has muddied the waters for voters, and many -- including the Irish prime minister -- admit they haven't even read all of the document they're voting on.
The Lisbon Treaty, as it is formally known, would create an EU president and foreign minister, and would slim down the EU Commission from 27 to 18 members, with rotating membership, to speed up the commission's work.
The treaty would also give national parliaments veto power over proposed changes and would assign voting weight to EU member countries.
Ireland's constitution requires that its citizens be given the chance to vote on anything affecting the Irish constitution, which in this case is the EU treaty.
It means Ireland's 3 million voters will decide on a document representing the 490 million people in the European Union.
After voters in the Netherlands and France rejected a previous EU constitution in 2005, no other EU country dared to put such matters to their voters, instead pushing it through their national parliaments. Dutch and French voters have no direct say on the current treaty.
If a majority of Irish voters cast "yes" votes Thursday, then Ireland will ratify the treaty.
Ireland is the only EU country that requires a referendum on the treaty; in the other 26 countries, the parliament decides. Eighteen EU countries have ratified the treaty so far; a decision is pending in the other nine countries, including Ireland.
The treaty will only come into effect if all 27 nations ratify it, something member states have said they want to happen in January 2009.
Officially, a "no" vote would mean the EU would continue to operate under present rules -- but in fact, it would bring chaos to the organization. European leaders would have to decide whether to draw up another constitution -- which would mean years of meetings and drafts -- or they would ask the Irish people to vote again.
This week, Ireland's Sunday Business Post reported a slight lead for the "yes" camp with 42 percent of voters supporting the treaty and 39 percent opposed.
A poll published last Friday by the Irish Times said 35 percent of voters were opposed, 30 percent were in favor, and slightly more than a third of voters were undecided or would not vote.
Referendum results are expected to be announced Friday afternoon, a spokesman for Ireland's Referendum Commission said.
Irish voters who are against the treaty have said they oppose the rotating membership in the EU Commission, wanting instead a permanent seat for every member nation. They also oppose weighted voting, which they say is primarily based on population size and would therefore diminish Ireland's voting power.
Irish businessman Declan Ganley is among those say they're worried the new treaty threatens Ireland's low corporate tax rate of 12.5 percent, though the treaty maintains a national veto on taxation issues.
Ganley founded Libertas, a European Union think tank which says that "tax veto" would not necessarily apply.
Catholic groups have said they fear the treaty would affect Irish legislation on abortion and gay marriage, which are not permitted in Ireland. Catholic bishops have said the EU treaty would not affect decisions on abortion, though the treaty's effect on gay marriage is less clear.

The Irish Farmers' Association had concerns about the World Trade Organization cutting beef import tariffs, and though the issue had nothing to do with the treaty, the IFA urged its members to vote against it.
The farmers' group reversed its position this month, however, after it said Prime Minister Brian Cowen promised he would veto the cuts.
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