The difference between Irish and British steer prices has more than doubled since June, while the gap for heifers has almost quadrupled.
Latest official figures show that Irish beef finishers are being paid 84c/kg less for R3 steers and 77c/kg less for R3 heifers than their counterparts in Britain. The difference is equivalent to €302/hd for a 360kg steer and €252/hd for a 330kg heifer.
The ICMSA claim that the widening gap has cost Irish producers in excess of €10m over the past three months.
The ICMSA's livestock chairman, Michael Guinan, said that Irish processors and retailers were grabbing more of the margin than their British counterparts.
The statistics also show that Irish prices have fallen in recent weeks to their lowest level in over a decade, when compared to British prices.
At the beginning of June, suppliers of R3 steers to the Irish factories received more than 91pc of the British price for similar grade stock. By the first week of September, this figure had fallen to 81pc. The equivalent fall for R3 heifers was from 95pc to 82pc over the same period.
The price difference between Irish and British R3 steers in June was 36c/kg, less than half of the 84c/kg gap that exists now.
However, the change over the same period for R3 heifers was even greater, with the difference increasing four-fold from 22c/kg to 84c/kg.
"It is perfectly obvious that the squeeze being inflicted by the processors and retailers on their farmer-suppliers is actually getting worse. The Minister has a clear responsibility to address this continuing market-manipulation and margin-stripping," said Mr Guinan.
The ICMSA man queried why Irish beef exports into Britain declined during June, while export volumes into other countries increased.
"If Irish beef processors have been able to find other markets offering better returns, why have Irish farmers not seen the benefit of these returns?" he asked.
A spokesperson for Meat Industry Ireland said that an increase in British beef production resulted in slightly lower imports from Ireland in June and July.
"It is important that Ireland continues to develop and expand European and other markets to ensure we are not over-reliant on any one market," the body said in a statement.
"It must also be recognised that overall there has been an 11pc increase in Irish beef exports to Britain versus the same period in 2013," the statement added.
Taking the period from January through to September, Irish producers have been paid an average of 87pc of the British price. This compares with 97pc during 2008 and 96pc in 2011.
Heifers were 111pc and 99pc of the British average in 2005 and 2011, respectively.