'Lack of action' concerns raised over Welsh language
Banning large housing projects could be a way of halting a fall in the number of Welsh speakers in north and west Wales, a campaign group says.
Welsh Language group Dyfodol also says relocating Wales' national bodies to those areas could aid the language.
It follows a critical Council of Europe report on minority languages in the UK, describing the fall as "worrying".
In the 2011 Census, Welsh speakers dropped below half for the first time in Ceredigion and Carmarthenshire.
The Council of Europe report also highlighted concerns about the delivery of health and care services through the medium of Welsh.
It said: "There have been worrying falls in numbers of Welsh speakers in the traditionally strong areas of north and west Wales, with two counties becoming less than 50% Welsh-speaking for the first time in their history.
"Despite positive developments, there remains considerable concern about the situation on the ground with regard to offering health and social care services in Welsh."
Heini Gruffudd, chair of Dyfodol i'r Iaith (Future of the Language), said: "The report highlights the results of the last Census.
"In a way it brings attention to the lack of action on a community and county level regarding the number of Welsh speakers.
"The message is that planning practices in Wales have militated against thriving Welsh communities.
"We haven't succeeded in having sustainable communities."
He said while the Welsh government has housing targets in every part of Wales, some areas should either be on a small scale or left alone.
"If the houses were needed, they would just be filled by incomers rather than local people," he added.
Mr Gruffudd also suggested relocating national bodies who support the Welsh language to Welsh-speaking parts of Wales so that people do not have to move away for work.
Welsh language broadcaster S4C is already considering moving its headquarters out of Cardiff to either Carmarthenshire or Gwynedd.
In the 2011 Census, figures showed the number of people who speak Welsh has fallen in the past 10 years with it being a minority language in two heartlands, Carmarthenshire and Ceredigion.
It has been thought that migration trends and education might lead to an increase in speakers in less traditional Welsh-speaking areas.
But the census suggests otherwise, with just two areas, Monmouthshire and Cardiff, seeing a percentage increase.
Only in Gwynedd and Anglesey do over half the population now speak Welsh.
It has been a topic of concern which Cymdeithas yr Iaith Gymraeg (Welsh Language Society) and the Union of Welsh Independents, among others, have raised concerns over.
But a spokesperson from the Welsh government said it had taken several steps to address the issue of the decline in the numbers speaking Welsh including its More than Words strategy and it was awaiting for a report which looked at ways if increasing the numbers in areas where it was declining.
"These are just some of the steps we are taking and while we are committed to leading the way on facilitating the use of the language, everybody in Wales must recognise the important role they play in promoting the language and ensuring it thrives across Wales," said the spokesperson.
Meanwhile, Wales is not the only place to fall foul of the the report by the Council of Europe - which is a human rights organisation with 47 member states.
The Northern Ireland Executive has also been strongly criticised over how it promotes the Irish language.
Stormont failed to provide the council with information on the use of both Irish and Ulster-Scots, because the NI parties could not agree a submission.
The council's report said more should be done to promote Irish, including in NI's courts and the assembly.