The European Union on Friday issued 50 steps that Greece should implement to better control its borders within three months, in a process that could ultimately allow other European countries to maintain checks on migrants at their frontiers.
The continent has been struggling to get a handle on a migration influx that saw more than 1 million migrants and asylum seekers reach Europe last year - most of them through Greece.
Athens has been accused of letting people move through its territory largely unchecked. Its border with Turkey is an external frontier of Europe's free-travel Schengen zone.
The recommendations, endorsed by a majority of the bloc's member states, are aimed at addressing "serious deficiencies" in Greek border controls identified during unannounced inspections in November.
The Greek government voted against the decision Friday, while Cyprus and Bulgaria abstained, EU sources said on condition of anonymity. Athens issued a statement expressing regret at the decision.
"The massive mixed migration flow is of a nature that would put the external border control of any member state under severe pressure," the statement says, noting that Greece has taken measures to address the situation - at a "substantial national financial and social cost."
The 50 recommendations address the need for better identification, registration and fingerprinting of migrants arriving in Greece - including steps to spot fake IDs and issue tamper-proof documents; closer surveillance of sea borders; more equipment; and better training of border staff, among other things.
They include specifics such as issuing magnifying glasses to improve ID checks and the reallocation of a heart beat detector to spot stowaways in cargo shipments, as well as broader recommendations on improved cooperation with Greece's neighbours Turkey and Bulgaria.
Athens now has until May 12 to implement the measures. If it fails to do so, the European Commission could allow other Schengen countries to reinstate national border controls for up to two years.
Schengen usually is the epitome of free movement, allowing people to move through 26 European countries without the need for passports or border checks. But Austria, Denmark, Germany, Norway and Sweden have already reintroduced temporary controls to better manage migration surges.