Ireland will hold a referendum on the fiscal treaty agreed by 25 out of 27 EU nations in January, Irish Prime Minister Enda Kenny announced February 28.

The announcement was a surprise, as EU leaders tried to design the treaty so it would not trigger referenda. However, Ireland’s attorney general, Máire Whelan, said that “on balance” Ireland’s constitution requires one.

The referendum won’t stop the new treaty—it goes into force once 12 nations have approved it. But Ireland has a history of throwing a spanner in the works of EU treaties. It voted “no” to the Lisbon and Nice treaties, having to be asked again before it got the ‘right’ answer. This time, Ireland has said it will not hold a second referendum if the answer is “no.”

A no vote would cause the European Union to fracture even more. The United Kingdom and the Czech Republic have already opted out of the new treaty. The referendum could force Ireland to follow suit. This would put the EU in a tough spot. The Telegraph’s Ambrose Evans-Pritchard says that if Ireland votes no, the whole fiscal compact could fall apart. He writes that “it would be politically untenable to create a new eurozone structure that left one member in limbo.”

“The fiscal compact has totemic significance in Berlin, and any sign that the package is fraying may harden opposition in the Bundestag to further emu rescue measures,” he writes. A “no” vote could cause the whole compact to be torn up and a new agreement made, perhaps with an even smaller group of nations.

If, on the other hand, Ireland votes no and EU nations decide to leave it behind, the EU would also be further down the road to the 10-nation superstate that the Trumpet has long forecast.

Either way, a no vote would clearly demonstrate that even without the UK, such a large group of EU nations cannot push quickly toward integration.

Soon, a much smaller, core group will push toward much closer union.