Ireland's 'yes' to an EU reform treaty capped a two-decade, roller-coaster ride to expand the union after the Cold War and widen its powers.

The experience has been so troubled that relief in EU capitals was palpable when Irish voters approved the 2007 Lisbon Treaty on Saturday — 16 months after rejecting it in a first vote.

But there are still hurdles ahead.

Politicians in Poland and the Czech Republic question the legality of changes enacted to get Ireland on board. After the 2008 Irish 'no', Dublin won guarantees the EU will not gut its traditional neutrality, abortion ban or tax powers.

And experts say that even if the treaty is passed by all member nations, EU governments may lack the political will to take full advantage of reforms such as freer trade, a highly contentious issue in Europe.

A successfully reformed European Union would have a president, a single foreign policy chief instead of two, less red tape and a European Parliament with more power over legislation. For the first time, the assembly gets a say in drafting the EU budget that totals some $175 billion a year.

European voters able to collect 1 million signatures will be able force the EU to draft new rules. And if a country is fed up with the EU, it can leave the club unilaterally.

The Lisbon Treaty approved by Ireland Saturday is hailed as a big step toward an EU more effective, more accountable and ready to take on international issues — such as climate change, financial reforms and international trade — with the United States, China, Japan, Russia, India and other global players.

Pierre Moscovici, a former French deputy foreign minister, said the treaty alone will not lead to change, however.

"What if EU governments disagree on what fair trade means? There is clearly much work to be done by European political leaders, if they are to take advantage of the Lisbon treaty's full potential."

The structure of the EU has been the subject of nonstop debate for almost 20 years.

In the early 1990s, it was over a single currency and a common foreign policy.

This was followed by a tortuous, still ongoing wrangle over immigration matters as several governments are loath to cede border control to the EU. And then there was the drafting of a European Constitution, an overly ambitious undertaking that French and Dutch voters rejected in separate referenda in 2005.

"Europeans citizens are tired of these recurrent discussions" over European integration, Moscovici said.

He suggests a pause, saying endless tinkering with the EU has led to an "estrangement between the European Union and public opinions across Europe."

After the Irish vote, EU officials said they will push Poland and the Czech Republic to remove legal hurdles in those countries that prevent them from completing the treaty's ratification.

EU officials will meet with Czech Prime Minister Jan Fischer on Wednesday. Half a dozen Czech lawmakers have filed a legal challenge against the Lisbon Treaty that prevents President Vaclav Klaus from endorsing the parliament's ratification.

EU officials see political motives. "In the end, President Klaus will sign the treaty," European Commission President Jose Manuel Barroso said Saturday.

Last week, French President Nicolas Sarkozy warned of unspecified "consequences" for the Czech Republic if Klaus continues to withhold his signature.