The president of Ireland's largest trade union is calling for government action to prevent Irish banks hiking their mortgage interest rates.

Permanent TSB is planning to increase its standard variable rate by half a percentage point, blaming the high cost of funds, rising deposit rates and tight margins.

There is speculation that this might open the door for other banks to follow suit.

SIPTU president Jack O'Connor says the Government should take whatever action it can to block the move.

Mr O'Connor says these banks are being kept afloat by the Irish taxpayer and should not be allowed to engage in "immoral" behaviour that could further damage consumer confidence.

He says the Government should threaten to withdraw the State's deposit guarantee from any bank that hikes interest rates.