What is it?
Spearheaded by Swiss president and energy minister Doris Leuthard and drawn up partly in reaction to the 2011 nuclear reactor disaster in Fukushima, Japan, the energy strategy 2050 aims to gradually withdraw Switzerland from nuclear power and increase its use of renewable energy sources.
Under the plans no new nuclear power plants will be built in Switzerland and the five that do exist – including the world's oldest operating reactor, Beznau I – will be decommissioned at the end of their technically safe operating life.
The strategy will focus on exploiting hydropower and other renewable resources such as wind and solar power, as well as increasing energy efficiency by offering tax incentives for energy-efficient building works and tightening emissions rules for passenger vehicles.
These measures require changes to the existing energy law, and the first set were approved by the Swiss parliament last September.
Why a referendum?
Because under the Swiss system of direct democracy, anyone can challenge a new or revised law through a public referendum if they gather 50,000 signatures within 100 days.
The Swiss People's Party (SVP) did just that.
The right-wing party opposes the strategy, saying it will be too expensive, and is therefore campaigning for the Swiss public to vote against it on Sunday.
The SVP claims the strategy would cost each household 3,200 francs a year, a figure refuted by the government, which states a figure of just 40 francs.
The strategy is supported by the Socialists, the Greens, the Christian Democrats, the Liberal-Radicals and most other parties.
Didn't Switzerland already vote on nuclear power?
Indeed. Last November the Swiss rejected a popular initiative backed by the Green party which called for the country's nuclear power stations to be closed a lot sooner – three of them as soon as this year.
The government opposed the move, saying the deadlines proposed by the Greens were not realistic and did not allow the country enough time to replace nuclear power with renewable sources.
The public agreed, rejecting the plan by 54 percent.
At the time the SVP voiced hope that the outcome meant the Swiss people would also vote against the government's energy strategy. But that's currently looking unlikely...
Will this latest referendum pass?
At the moment it's on track. Back in April a poll showed 61 percent of voters would back the government's strategy.
Since then the margin has narrowed, however a Tamedia survey taken on May 10th still showed the ‘yes' camp in the lead on 53 percent.
Find out more about the energy strategy 2050 on the government's dedicated site.