Plans to change how social and private homes are rented in Wales have been outlined by the Welsh government.
Welsh Housing Minister Carl Sargeant said simpler tenancy agreements would make it easier for tenants and landlords to know their rights.
But a landlords' organisation warned the changes would significantly increase the costs to its members.
The Residential Landlords Association (RLA) argued the extra money would be better spent on building homes.
Local authority-owned rented properties currently operate under secure tenancies which allow tenants to live in their properties indefinitely.
Private rented and housing association tenants, however, are subject to assured shorthold tenancies.
These give tenants the right to occupy a property for a fixed period of time, but at the end of this the landlord has the right to terminate the tenancy.
Under the proposals many different forms of rental contract would be replaced by just two.
Housing Association properties would be brought into line with local authority-owned homes - meaning they would both operate under the secure tenancy regime.
Private rented homes would be on a "standard contract", similar to the assured shorthold tenancy.
The plans are based on recommendations made in April by the Law Commission, the statutory body which reviews the law.
Mr Sargeant said the new framework would provide a "fairer, more transparent and flexible system" that "has benefits for tenants and landlords alike".
"It will also help people in situations of domestic violence and in dealing with the anti-social behaviour of some households," he said.
"These proposals will create a level playing field for all landlords and also provide a fairer deal for tenants, irrespective of who they rent their home from."
But the RLA believes the reforms will cause a significant rise in legal and administrative costs for landlords.
"The laudable intention of the government's proposals, namely simplification, are ones which we wholeheartedly share," said Douglas Haig, RLA director for Wales.
"In our view, tenure reform can be achieved in a less radical way and without the huge upheaval and expense involved for landlords, tenants and others involved in all sectors of rented housing including the need to re-learn and re-skill across the board as a result of a completely new system."
He added: "The millions that would be spent on the Welsh government's proposals are simply too high at a time when that money could be much better spent on building more homes."
Shelter Cymru director John Puzey welcomed the proposals as "a really important step forward".
"Some of the law associated with tenure dates back hundreds of years so the proposals to simplify contracts and establish two clear forms of tenure will benefit tenants in both the private and social sectors.
"Almost a third of our casework comes from people who live in the private rented sector.
"This is a hugely disproportionate level of work given the size of the sector in Wales, but at base many of these problems are due to a lack of understanding about rights and duties by tenants and landlords alike," he added.
A three-month consultation has now begun with a bill due to be introduced in the assembly in 2015.