ZURICH (Reuters) - Swiss voters would rather maintain close economic ties with the European Union than adopt immigration curbs that could jeopardize Switzerland’s access to the EU single market, a survey published on Sunday showed.

The issue is the thorniest political issue in Switzerland’s relations with the EU, its biggest trading partner. The 28-nation bloc insists on maintaining the principle of free movement of people, as enshrined in bilateral accords with Switzerland.

The Swiss parliament last month dodged a conflict with Brussels by adopting a system of giving unemployed locals hiring preference over EU nationals instead of imposing immigration quotas, as Swiss voters had demanded in a binding 2014 referendum.

In a poll of 1,000 people conducted by OpinionPlus for the SonntagsBlick paper, 47 percent said they would again vote for immigration curbs as in 2014 versus 43 percent against.

But 52 percent opposed a campaign by a right-wing isolationist group to end the free movement rules that underpin bilateral accords permitting Swiss access to the EU single market, with only 30 percent in favor, the poll found.

If forced to choose between immigration curbs and the bilateral accords, 54 percent backed the accords and 41 percent wanted immigration quotas, with 5 percent unsure.

The Swiss approach to resolving the conflict is being scrutinized for hints of what Britain might expect as it negotiates the terms of its divorce, or ‘Brexit’, from the EU after its own referendum last June.

Under the Swiss system of direct democracy, how voters view the issue remains very important.

The SonntagsBlick newspaper also quoted Albert Roesti, head of the right-wing Swiss People’s Party (SVP) that champions immigration limits, as saying the question in the poll was wrongly formulated.

“We are convinced that we can implement the (2014) mass immigration initiative without the EU suspending the bilaterals,” he said.

The SVP has said existing bilateral economic accords were too valuable to the EU for Brussels to annul them, while EU leaders have stressed they cannot show leniency to non-EU member Switzerland without encouraging hardline Brexit negotiators.