By Caroline Copley

BERNE (Reuters) - Drastically limiting immigration in Switzerland would isolate the country by damaging its ties with the European Union, left-wing groups said on Monday, calling on voters to reject the proposal.

Swiss voters will decide in a referendum on Nov. 30 whether they want to cap immigration at just 0.2 percent of the resident population or the equivalent of 16,000 people per year.

In 2013, net immigration was five times greater at 82,800, according to the office for national statistics.

The initiative "Stop overpopulation - safeguard our natural resources" launched by the environmentalist group "Ecopop" comes after voters narrowly backed a right-wing proposal in February to introduce quotas on EU citizens, triggering strong criticism from Brussels.

Opponents say a vote for the far more restrictive "Ecopop" measures would sound the death knell for Switzerland's bilateral accords with the EU, which govern trade, agriculture and economic and technological co-operation among other things.

Free movement of people is one of the fundamental policies of the European Union, and Switzerland, while not a member of the 28-nation bloc, has to uphold that principle in order to benefit from favorable trade conditions.

The Swiss government is still working out how to implement February's vote. Draft legislation in June to reintroduce quotas on EU citizens from 2017 was denounced by the bloc.

"The first and most important step against Switzerland's political isolation is a clear and significant rejection of the Ecopop initiative," Regula Rytz, co-president of the Green Party told a media conference in Berne.

"Ecopop blames the global environment problems on the number of people and not the wasteful lifestyles of industrialised and emerging countries," she added.

The Ecopop campaign says a lack of living space exerts too much pressure on the land and natural resources in landlocked Switzerland, which has a population of over 8 million.

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The "No to Ecopop" committee, which comprises 35 political parties, trade unions and migrant groups, said the proposals would lead to more short-term workers and cross-border commuters putting pressure on wages and leading to greater pollution.

Still, the Ecopop campaign taps into a growing concern about overcrowding among residents of Switzerland who are frustrated by rising rents and crowded public transport.

The initiative, brought after Ecopop gathered the necessary 100,000 signatures to force a national vote under Switzerland's practice of holding referendums, also calls for the earmarking of 10 percent of Swiss development aid budget for voluntary family planning, which opponents said was counterproductive.

"We need to fight poverty by giving individuals human rights and by improving their social, economic and ecological environment," said socialist lawmaker Ada Marra. "And not by handing our contraceptives."

(Editing by Alison Williams)