Vulnerable tenants living in buy-to-let properties are being evicted by sheriffs when owners fall into arrears.
Housing charity Threshold revealed it receives two or three calls a week from desperate renters caught up in the crossfire between landlords and financial institutions.
Senator Aideen Hayden, Chairperson of Threshold, said with one in three buy-to-let properties in mortgage default, many tenants are left at risk. "There is a huge issue here that has to be addressed," she warned.
Bob Jordan, charity director, said financial institutions sometimes ignore the rights of tenants in their pursuit of the landlord's assets.
"A worrying new phenomenon is the appointment of rent receivers by lending institutions, to bypass landlords and collect the rent directly from tenants," he said. "The first time the tenant hears about it is when a sheriff knocks on the door to repossess the property.
"In the past 12 months, we have dealt with an increasing number of cases where tenants have been threatened with eviction by both their landlord and a rent receiver if they do not hand over the rent to either party. This places the tenant in an impossible position."
Threshold's annual report showed more than 23,000 people needed assistance in 2011.
It said since the economic crisis, employed and the unemployed are competing for the limited pool of rented properties, leaving first-time renters and vulnerable tenants susceptible to rogue landlords.
More than 3,200 queries related to the illegal retention of tenants' deposits by landlords, which is estimated to be worth up to 2 million euro.
"Deposit retention has become one of the greatest barriers to the smooth operation of the private rented sector," Mr Jordan added. "While landlords are entitled to keep deposits in certain circumstances, almost 80% of deposit disputes that go before the Private Residential Tenancies Board result in some or all of the money being returned to the tenant, proving that most landlord claims are not legitimate."