Poland's direct interest is to help save the struggling euro zone, and respectively to back the newly proposed EU treaty for a European fiscal union, according to Polish Prime Minister Donald Tusk.

Tusk defended Thursday his government's backing of an EU treaty for closer fiscal union, during a debate in parliament where his government faced a no-confidence motion by the right-wing opposition, DPA reported.

"You don't have to be an economist to see how events in the euro zone directly affect the (Polish) zloty," he said, referring to the fact that Poland does not use the euro.

The opposition Law and Justice Party says the new treaty, which is backed by Tusk's liberal conservative Civic Platform party, undermines Polish sovereignty.

It has submitted a no-confidence motion against Tusk's foreign minister, Radoslaw Sikorski, who is strongly in favour of boosting the powers of the European Commission to supervise government spending and budgets of member states.

The opposition argues that a speech by Sikorski in Berlin last month, in which he said Poles were "ready to renounce a part of Polish sovereignty," was unconstitutional.

DPA points out is almost certain to fail, given that the ruling coalition has a majority in parliament. But it highlights growing division in Poland over the new EU treaty. Recent polls have shown an 8% rise in the popularity of Law and Justice.