LJUBLJANA, July 4 (Reuters) - Slovenia's parliament voted on Tuesday to put the government's flagship infrastructure project, a 1 billion euro ($1.1 billion) rail link, to a referendum on Sept. 24.
The 27-km (17-mile) line is designed to speed up freight traffic between the city of Divaca and Slovenia's state-owned Adriatic seaport at Luka Koper.
The lobby group Taxpayers Don't Give Up and the main opposition party, the centre-right Slovenian Democratic Party, had pushed for the referendum, arguing that the line, as projected by the government, was too expensive.
The centre-left government has already won 44.3 million euros of European Union funds for preparation of the track, while landlocked Hungary had said it is ready to invest about 200 million euros as it relies on Koper for much of its sea freight.
A rejection by voters would put the project on hold for at least a year, and most likely longer as a parliamentary election is due in mid-2018.
However, for a rejection to be valid, it needs not only a majority of those voting, but also the backing of at least 20 percent of the 1.7 million or so eligible voters.
"We believe the project is of strategic importance to Slovenia ... as it will have multiplicative effects on the economy," Infrastructure Minister Peter Gaspersic told parliament before the vote.
An opinion poll published by the daily Delo on Monday indicated that 56 percent of those who planned to vote would reject the project, but left unclear whether enough voters would turn out to make the rejection binding. ($1 = 0.8815 euros) (Reporting By Marja Novak; Editing by Kevin Liffey)