Several hundred Swiss Post employees have launched a series of public protests against planned job cuts and a controversial restructuring programme.
The demonstrations in three cities across the country come ahead of a new round of negotiations next month.
Trade union leaders said they would not give up their industrial action until they won assurances from the management that nobody would lose their jobs or have to accept salary cuts.
In October Swiss Post announced it would be slashing up to 500 jobs over the next two years as part of a major overhaul of the postal network in a bid to remain competitive in an increasingly liberalised market.
Christian Levrat, leader of the trade union of postal workers and parliamentarian, said Monday's protests in Lucerne, Neuchâtel and Lugano were the beginning of a series of actions in the next few weeks to force management to back down.
"Firing people and salary cuts are unacceptable for a company that made a profit of nearly SFr1 billion ($0.83 billion) last year," he said.
He added that the unions were also considering stronger forms of protest ahead of Christmas if the Swiss Post management was unwilling to change its reform plans. However, he did not elaborate.
The state-owned company has a workforce of 55,000 and is the biggest public employer in the country.
The management criticised the protests ahead of negotiations on a social plan. It added that it was ready to seek solutions for its employees directly affected by the restructuring.
Swiss Post's chief executive Ulrich Gygi said the cuts in the postal network were not negotiable. However, he said he remained convinced that it was possible to find a compromise with the unions, according to newspaper reports.
He said no postal employee would lose his job as a result of the reorganisation.
"We will find a solution and I'm convinced that all Christmas presents will be delivered in time," he said.
Switzerland's postal network is relatively dense with 35 post offices per 100,000 people – twice as many as in neighbouring Germany.
Under the restructuring programme post services will be revamped. Dozens of post office agencies will be downgraded and situated within existing shops, such as village stores.
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Swiss Post is a state-owned company with a workforce of about 55,000 making it the largest public employer. It continues to provide a nationwide public service but also engages in competitive business.
It was originally established in 1849 and from the beginning the federal institution was responsible for transporting passengers, letters, parcels and money.
As part of the market liberalisation, the Post Office lost its monopoly on letters weighing more than 100 grams.
Politics continues to exert a substantial influence on the company. The government sets strategic goals for Swiss Post and monitors them every year.