UN urged French seaside towns and resorts that had adopted similar bans "to repeal them immediately."
It "would be unconstitutional, ineffective and likely to create antagonism."
The burkinis did not pose any threat to public order, said the council, which is France's highest administrative court.
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"If anything, [the ban] is more likely to alienate and upset moderate Muslims."
The world market for Islamic clothing was estimated at $230 billion in 2014 and could reach $320 billion (280 billion euros)...
The ban was decided out of "respect for good customs and secularism", a founding principle of the French republic.