Gwynedd councillors have approved a plan for 8,000 houses in north Wales over 15 years.
The Local Development Plan includes some houses which have already been built or have planning permission, but it would mean 1,366 new homes in Gwynedd in nine years.
About 50 people protested outside the council chamber on Friday saying it would affect the Welsh language.
Anglesey council will vote on the plan, which affects both counties, on Monday.
The Gwynedd council vote was tied 30 to 30 with four abstaining, but with the chair in favour the proposal was passed.
Cabinet member Dafydd Meurig said in some parts of the county, particularly in the Llyn Peninsula, only people with local connections would be able to buy houses.
One councillor, Alwyn Gruffydd of Llais Gwynedd, agreed with the campaigners, saying approval would make councillors "traitors".
Some councillors had argued the decision should be delayed but were told this was not possible as the plan had to be accepted or rejected within eight weeks of a Welsh Government report.
Menna Machreth, from Cymdeithas yr Iaith Gymraeg (Welsh Language Society), had appealed for councillors to reject the plan, saying it would damage the language.
The society has now urged Anglesey councillors to reject the plan.
"It's clear that the housing targets that are forced on local councils are unfair and linguistically unsustainable," Ms Machreth said.
Council leader Dyfrig Siencyn said: "The plan we have approved is based on comprehensive evidence regarding the matters which are most important for local people - housing which includes affordable housing, jobs and the Welsh language.
"Crucially, in some coastal communities where the price of most houses are beyond the reach of local people, it includes an innovative local housing market policy - the first of its kind in Wales - which will ensure that any new homes are based on local needs."
The report going before Anglesey councillors on Monday also recommends adopting the plan.