The Conservatives say they will not support a bid for more Welsh powers on housing unless two clauses are removed.
It comes as a call was made for cross party unity to tackle homelessness by Secretary of State Peter Hain.
Mr Hain is urging all parties to back a bid from Wales for more housing powers before the dissolution of parliament.
But the Tories object to clauses to suspend the right to buy and one which they claim could allow Gypsy sites to be built contrary to local decisions.
MPs are due to scrutinise a legislative competence order (LCO), or Welsh law, on housing.
Mr Hain said it was important that it was approved in order for commitments on housing in Wales to be delivered.
"There is widespread consensus that this wide-ranging LCO is urgently needed to tackle Wales' housing problems," he said.
"Although the number of people presenting themselves as homeless fell by 3% to 1,475 in the last reported quarter there are still thousands of 'hidden homeless' people in Wales who need urgent help.
"This LCO would not only give the assembly powers to update and improve the way in which social housing is allocated and regulated in Wales but it would also allow them to increase the supply of affordable housing and to help prevent homelessness.
"If the LCO fell at this late stage, it would be a huge blow for homeless and vulnerable people in Wales."
He said that housing organisations across Wales were supporting the bid for Wales to get more powers over the issue.
"This LCO could be agreed in the wash-up negotiations between the parties which will precede the dissolution of this Parliament.
"But only if it is agreed by all parties. I call on the Conservatives to join the cross-party consensus, listen to the voluntary sector and support the housing LCO."
But the Conservative party says it will not support the bid until two clauses have been removed.
David Jones, Clwyd West MP and shadow minister for Wales, said: "The Conservative party has two fundamental objections to the proposed order.
"In the first place, we oppose any proposal that could lead to the abolition of the right to buy that is currently enjoyed by Welsh social housing tenants.
"The right to buy has greatly facilitated social mobility in Wales and is valued by politicians of all parties, including the former Secretary of State, Paul Murphy.
"The assembly government has confirmed that it does not intend to abolish the right to buy and therefore there is no reason why it should not agree to have the power to do so excluded from the LCO.
"Secondly, the LCO in its present form could potentially give the Welsh Assembly Government the right to impose the location of Gypsy and traveller sites upon local communities contrary to the wishes of local authorities.
"We believe that that would be undemocratic and that such decisions should be taken locally."
He said that if the two clauses were removed from the LCO, the party would support it.
Mr Jones said he had written to Wales Office minister Wayne David to clarify the Conservative party's position on the matter.