(WARSAW) - Poland's Senate approved the EU's Lisbon Treaty Wednesday, marking the final step in Warsaw's ratification of the accord meant to streamline the 27-nation bloc.

A total of 74 members of the upper house backed a bill from the liberal government authorising President Lech Kaczynski to sign the treaty into law, while 17 voted against and six abstained.

The Senate vote came a day after the Sejm or lower house overwhelmingly backed the treaty, after a deal to end weeks of wrangling between Prime Minister Donald Tusk and the eurosceptic opposition.

The Lisbon Treaty, which replaces the EU constitution scuppered by French and Dutch voters in 2005 referendums, has to be ratified by all 27 member states if it is to take effect by the 2009 target.

For several weeks it had appeared that Poland, the largest of the ex-communist newcomers to the EU in 2004, could upset the reform process this time.

Tusk, the president and his twin brother, opposition leader Jaroslaw Kaczynski, had spent much of March battling over the ratification bill.

The Kaczynskis had demanded additional legal guarantees, saying they were needed to protect Poland's interests in the EU.

They notably bashed the Charter of Fundamental Rights, tied to the Lisbon Treaty, arguing it could open the door to same-sex marriages in Catholic Poland and the restitution of properties lost by Germans after the Polish-German border was redrawn by World War II Allies in 1945.

Their stance drew criticism, as both brothers had been involved in drafting the EU treaty last year, before Jaroslaw Kaczynski lost office to Tusk in a snap election in October.

Last year, the twins had trumpeted the treaty as a success and claimed it was only thanks to their confrontational style that Poland, like Britain, secured an opt-out from the charter, a wide-ranging accord on human rights and freedoms.

The Kaczynskis argued Tusk's bare-bones ratification bill failed to adequately protect the opt-out, and threatened to torpedo ratification outright.

Tusk in turn warned he could call a referendum should the bill fail in parliament -- and opinion surveys suggested 65 percent of Poles would back the treaty.

After realising they were out of step with the public, the Kaczynskis struck a deal with Tusk last weekend.

Under that compromise, the Sejm also approved a non-binding resolution addressing the conservatives' concerns.

It reaffirmed the supremacy of the Polish constitution over EU legislation, and also stressed the Christian roots of Europe, a reference the Kaczynskis had failed to convince other EU member states to include in the Lisbon Treaty.

The treaty, adopted by EU leaders in December, is designed to smooth the running of the bloc, whose membership has almost doubled since 2004.

Lawmakers in Bulgaria, France, Hungary, Malta, Romania and Slovenia have already ratified it.

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