The Romanian parliament has overwhelmingly voted to give NATO unlimited use of the country's airspace to pursue its campaign against Yugoslavia.
President Emil Constantinescu told deputies they must grant the request if Romania was to join NATO and the European Union in the near future.
Correspondents say there is public unease about NATO's request.
Yugoslavia has said the move would violate the two countries' treaty of friendship.
The Bulgarian parliament is due to vote on a similar request, probably next week.
The Czech Republic and Slovakia have granted permission to NATO to transport ground forces across their territory. This means there is now a land corridor for NATO to move troops from Germany to Hungary, which borders on Yugoslavia.
From the newsroom of the BBC World Service