The Irish Property Owners' Association has said landlords consider the new rent rules as unjust, unfair.
It said rent reviews every two years appear to be unconstitutional.
Yesterday, the Government announced its 'New Deal for Tenants', which, along with the two-year rent review, also includes increased notice periods for rent reviews and much greater protection for tenants.
Minister for the Environment Alan Kelly said the legislation will be introduced as quickly as possible.
Speaking on RTÉ's Morning Ireland, the association's Information Officer Margaret McCormack said the IPOA is seeking legal advice on whether or not they will challenge the measures.
She described it as "an unjust attack on the property rights of one group of people for the benefit of another without allowing the first group to be fairly compensated".
She said it will cause more landlords to leave the sector and that 30% of landlords want to leave the market altogether.
She said once we lose these people, "we're losing all these properties from the market".
Ms McCormack said the biggest problem tends to be that rent supplement is not set at a market rate and because of that, people in receipt of the supplement are not able to look for properties on the same level playing field as everyone else.
Minister Kelly said it will be illegal for landlords to increase rent between now and the introduction of the legislation unless a rent review is due or, if under the terms of the tenancy, the rent has not been increased in the last year or two and a rent review is due.
He said if this happens a tenant can refer it to the Private Residential Tenancies Board (PRTB) and the rent will be frozen while the issue is dealt with.
He said the PRTB will be given extra staff and extra power.
He said his intention is to give the PRTB more power to "police certain aspects of the landlord-tenant relationship".
Mr Kelly said: "If a landlord feels now that they can increase rent dramatically and ensure they cover for instance, as some commentators are saying, the two-year window, no they can't, that would be illegal.
"Any tenant who feels that a landlord is going to do this in the next week or so, refer it to the PRTB, once it's referred to the PRTB, the rent will be frozen as is and I can assure you the PRTB will deal with that issue and deal with that landlord".