LUXEMBOURG, July 10 (Xinhuanet) -- Citizens of Luxembourg went to the polls starting Sunday morning to vote on the European Union (EU) constitution treaty.

    The referendum in the Grand Duchy will be the first since EU leaders announced a "period of reflection" on the constitution at their June 16-17 summit. A number of EU member countries have postponed their ratification plans and threw the future of the charter into serious doubt.

    The polling stations opened at 8:00 a.m. local time (0600 GMT) Sunday here and the preliminary results of the referendum are expected to be revealed soon after the voting ends in the afternoon.

    Support for a "yes" vote keeps slumping in recent months, especially since French and Dutch voters rejected the constitutionin referendums a month ago.

    The last opinion poll in mid-June showed that the public support for a "no" vote has risen to 45 percent, from 24 percent in October, while backing for a "yes" fell from 72 percent to 55 percent.

    Like the Netherlands, the Luxembourg popular vote is only consultative, but the parliament has promised to respect the wishes of the electorate.

    Speaking Friday night at a final campaign meeting, Luxembourg Prime Minister Jean-Claude Juncker admitted the vote would be close.

    "I cannot say that I am confident. I remain concerned about theLuxembourg people's willingness to say 'yes'," he said, adding "Ifthey say 'no', then the constitution will be buried. But I hope that we can revive it."

    The Europe's longest-serving head of government has vowed to step down if the country votes against the constitution.

    A total of 12 countries within the EU have so far ratified the constitution, and only one by popular vote with all the others endorsing the treaty through national parliaments.

    The treaty, designed to make the expanded bloc more effective in decision-making, among other EU treaties, has to be ratified byall 25 members for it to come legally into force. Enditem