Language campaigners at the rally in Caernarfon

Cymdeithas yr Iaith Gymraeg - the Welsh Language Society - argued that rising house prices were destroying the communities, along with the language.

Leader Huw Lewis told a Caernarfon rally that, under present trends, no such communities would be left by 2020.

The Welsh Assembly Government has said it has a "very strong" record in promoting the language.

The pressure group has pledged to step up action for a new language act.

"Our communities are under a great deal of pressure," said Mr Lewis.

"Over the next few years, communities across Wales could lose a range of vital recourses - their shops, their local schools and, of course, their houses - leaving those communities in totally unsustainable condition.

Property act

"One of the main elements of the crisis facing our communities is the constant inability of local people to gain access to the housing market."

Mr Lewis repeated the Cymdeithas call for a property act for Wales.

Cymdeithas members have been collecting signatures on a petition calling for legislation, which will be presented to the Welsh Assembly Government later this week, when AMs discuss the question of affordable housing.

Earlier this month, Cymdeithas vowed to step up their campaign of "direct action," demanding stronger legislation to protect the language.

First Minister Rhodri Morgan, who was the target of protests by Cymdeithas at the National Eisteddfod in August, has warned against "bullying tactics."

Mr Morgan told protesters that they would have to "learn the hard way" that such demonstrations would not influence his opinions.