Proposals to be announced on Monday could end the six-month notice period landlords must give.
More than a million people now live in rented properties in Wales.
A Welsh government spokesman said it would "improve and simplify the law" for tenants and it had consulted widely on the proposal.
While the majority of people in Wales still live in social housing, the private sector is expected to outgrow it within the next five years.
There are already parts of Wales where the number of privately rented homes outnumber social housing properties including Cardiff, Ceredigion, Conwy, Denbighshire, Powys and the Vale of Glamorgan.
But the standard of privately rented properties can vary greatly, partly because the law surrounding rental homes is so complex.
The Welsh government's answer is its Renting Homes Bill due to be launched on Monday.
Dr Bob Smith, a housing expert from Cardiff University, said: "There have been issues about needing to better regulate the private sector and they were addressed by legislation introduced last year (Housing Wales Act).
"The Renting Homes Bill is much more concerned with simplifying contractual relationships between landlords and tenants."
The bill is expected to outline a number of measures to set out the rights and responsibilities of landlords and tenants, and to make the process of renting easier.
It includes the introduction of just two tenancy types - one for social housing and one for the private sector - a more flexible approach to joint tenancies and standardised succession rights.
Steve Clarke, managing director of Welsh Tenants, which represents those in private and social accommodation, said it had been a long time coming.
"What this will attempt to do is to simplify the law so everyone understands their rights and obligations better," he said.
But there is concern it could include a plan to remove the protection private tenants currently have against so-called "no fault" evictions in the first six months.
John Puzey, director of Shelter Cymru said: "The idea of removing it is an extraordinary proposal. It will mean we will have the most insecure form of private tenure in the whole of Western Europe in Wales."
Elle McNeill, policy officer with Citizens Advice Cymru, believes there is a risk it could lead to an increase in evictions.
"Our concern is that it removes what little security there is at the moment in the private rented sector," she said.
"That's not to say that landlords will start evicting people immediately, it's that they could do if they wanted to."
But landlady Liz Davies, from Newport, believes scrapping the six-month term will give landlords and tenants greater flexibility.
"Landlords' hands are tied with having to give someone a six-month tenancy," she said.
"What tenants have to understand is that they are financially obligated for those six months."
"To think that I could potentially uproot the children, move somewhere and then be asked to move within six months, that is really worrying."
Rebecca has been asked to leave two properties unexpectedly over the past five years because landlords wanted to give the houses to relatives.
She wants to see the new legislation go further to give tenants better protection.
"In the social housing sector for landlords to obtain an eviction they have to show their actions are proportionate." she said.
"I really feel the same level of consideration should be given to those in the private rented sector."
A Welsh government spokesman said its aim was to improve and simplify the law and its consultation on the bill had received considerable support from a number of housing agencies.
Eye on Wales, is on BBC Radio Wales Sunday, 8 February at 12:30 GMT.
Plans to renovate the rental sector in Wales could mean less security for private tenants and an increased eviction risk, it has been claimed.