The US has this week increased the tariff on imported butter to the tune of an extra $.51c/kg.
The move increases the tariff on EU butter and, of importance to Ireland, its key co-operative Kerrygold brand by almost a third.
The tariff comes into effect immediately, and affects all countries without a free trade pact with the US and will run to at least the end of December 2015.
Current tariffs on this key dairy category for Ireland now stand at $2.05/kg.
Responding to the move by the US ICOS has questioned the commitment of the US to negotiating a fair and balanced TTIP dairy deal after it introduced additional duties.
ICOS has queried the move with officials both in the European Commission and also in the World Trade Organisation.
"While it does indeed seem to be legal, it certainly does not match the US rhetoric of opening free trade between Europe and the US, and certainly sends a bad signal in agriculture as the TTIP negations are set to ramp up a gear," it said.
Kerrygold butter has reached the number three position in the US market, up from fifth place at this time in 2014
According to Ornua, this is due to Kerrygold butter revenue increasing by over 60% in the last 12 months.
ICOS said Kerrygold butter has been making massive strides in the US under an ambitious strategy developed by Ornua.
"This no warning or no consultation imposition of a punitive tariff flies in the face of the US government’s stated positions on the matter.
"This is made even more galling when the price of US butter remains incredibly robust because of improved consumer perception, in spite of recent difficulties in the world dairy market," it said.
ICOS has also committed to working towards dismantling of this tariff over the coming months.