Diplomats from 25 nations including Britain have delivered a letter of protest to Iceland's government over its resumption of commercial whaling.
Norway says reaction "has been mixed"
British ambassador to Reykjavik, Alp Mehmet, was joined by counterparts from European and American countries.
The diplomatic "demarche" says Iceland should respect the global moratorium on commercial whaling and reverse its "unnecessary" decision of last month.
Iceland says it has received support from some other countries.
The demarche follows other diplomatic moves, including the summoning of Iceland's ambassador to London by the UK's marine affairs minister, Ben Bradshaw, and a protest by the US ambassador to Reykjavik.
Iceland announced in mid-October that it intended to resume commercial whaling, becoming only the second country after Norway to hunt the "great" ocean-going whales for openly commercial purposes since a global moratorium was imposed in 1986.
"This united action shows the depth of feeling and concern not only in Britain but all over the world about this cruel and abhorrent activity," said Mr Bradshaw.
"Today's protest leaves Iceland in no doubt about the strength of feeling against its decision to side-step an international agreement to stop the killing of whales.
"It has done great damage to its reputation and image."
But Iceland's whaling commissioner, Stefan Asmundsson, told the BBC News website he was not too concerned.
"We have always known there are mixed opinions when it comes to whaling," he said. "Reaction has been mixed, and we have received support from nations which agree with us that utilising whales on a sustainable basis is a reasonable thing to do.
"There have been diplomatic protests before to other nations engaged in whaling, but that has not resulted in any breakdown in diplomatic relations."
THE LEGALITIES OF WHALING
Objection - A country formally objects to the IWC moratorium, declaring itself exempt
Scientific - A nation issues unilateral 'scientific permits'; any IWC member can do this
Aboriginal - IWC grants permits to indigenous groups for subsistence food
Last year anti-whaling nations sent letters of protest to Norway and Japan, the countries which catch the largest numbers of whales.
The problem for the anti-whaling bloc is that on almost every other significant issue, including other environment issues, they side with Norway, Japan and Iceland, making stronger diplomatic action difficult.