The US Federal Aviation Administration (FAA) has downgraded the status of Thai aviation to Category 2.
Previously, Thailand's aviation industry was classified Category 1, allowing its carriers to fly to the US and to launch new services.
But in a statement posted on its website today, the FAA said: "A reassessment in July 2015 found that Thailand did not meet international standards."
Category 2 means that a country's airlines cannot open any new routes, but are allowed to operate existing services, although these will be closely monitored.
For passengers flying to/from the US, the move is largely irrelevant.
Thai Airways no longer flies to anywhere in North America, after axeing its sole transpacific route, between Bangkok and Los Angeles, in October (see news, July 23).
And no other Thai airline has the long-haul aircraft capable of mounting a transpacific service to the US.
But the FAA's announcement could cause knock-on effects elsewhere in the world as Thai Airways, the only Thai airline to fly long-haul to Europe, remains an important Asian airline in this continent.
For instance, Cologne-based European Aviation Safety Agency (EASA) tends to take note of US ratings. That was the case with Philippine Airlines - although downgraded to Category 2 by the FAA, it was banned from EU airspace for a number of years.
However, when the FAA similarly downgraded Indian aviation to Category 2 for 16 months last year (see news, February 2014), no similar action was taken by the EU authorities.