The Italian Senate on Wednesday rejected a motion by one of the ruling coalition parties, the Five Star Movement (M5S), to block an alpine rail link with France, paving the way for the controversial project to continue.
The planned line, meant to connect the Italian city of Turin with Lyon in France, includes a 58-kilometre tunnel through the Alps.
It is fiercely opposed by M5S but supported by its coalition partner, the right-wing League, and by most other parties in parliament.
The upper house of parliament rejected the M5S' motion by 181 votes to 110.
M5S is the largest party in parliament but it was outvoted by the combined forces of the League and opposition parties from the left and right.
A subsequent motion by the opposition Democratic Party, in favour of the project, was passed by 180 votes to 109.
The train link is one of several issues that has caused tension between M5S and its far-right government coalition partners in the League.
M5S has long been against the project on cost and environmental grounds but League leader and Deputy Premier Matteo Salvini is strongly in favour.
Premier Giuseppe Conte recently said it should be completed, arguing it would cost more to abandon the project.
Coalition 'at risk'
Salvini has warned that "those who say no to the [project] put the government at risk".
While M5S has accused the League of disloyalty by forming a block with the opposition, the rightist party said M5S would be to blame for any rupture in the coalition.
"Those who vote no today take the political responsibility for the choices which will follow in the coming days and months," said the League's Senate leader Massimiliano Romeo, in a thinly veiled threat to bring down the government.
The decision to resume the infrastructure project sparked protests last month, with thousands taking to the streets.
According to a recent poll, 70% of Italians support the construction of the new rail link.
When it is completed, the journey time between Milan and Paris will be cut from nearly seven hours to just four hours.