In the biggest nationwide strike in 55 years, construction workers downed tools on Monday at more than 100 building sites across Switzerland.
Around 15,500 workers protested in favour of lowering the retirement age to 60. The employers described the strike as illegal.
"This has exceeded our expectations," said Vasco Pedrina, president of the construction workers' union, who earlier told swissinfo that the strike was the biggest strike by construction workers since 1947.
Participation in the one-day stoppage was particularly strong in the French- and Italian-speaking regions.
Organisers said around 3,000 workers joined the strike in Geneva, while a similar number followed suit in canton Ticino.
Hundreds of builders also stopped work at major construction sites in Zurich, Basel, Bern, Lucerne and eastern Switzerland.
About 2,000 workers blocked a key road tunnel along the A1 in Aargau for about an hour, bringing traffic to a halt.
The Swiss Construction Federation (SCF), which represents employers, confirmed that around 100 sites across the country had been hit by industrial action.
However, employers described union claims that 15,500 workers had joined the strike as "propaganda", saying that only about 4,500 people had participated.
They added that the strike was illegal: "This is not a real, voluntary strike," said Daniel Lehmann, director of the SCF.
Unions say they will not alter their position when negotiations resume on Thursday and they have threatened to escalate the strike if no progress is made.
"We are not planning to fire all our shots at once," said Pedrina. "If this doesn't work then we will strike again - only next time it will be even bigger."
Jean-Luc Nordmannn, head of the State Secretariat for Economics Affairs, urged both sides to return to the negotiating table.
He said a solution was unlikely to be found on the streets.
The dispute centres on an accord negotiated in March allowing those working in the building industry to retire at 60 - five years earlier than normal.
Construction workers have long been calling for an earlier retirement age because they say that half of those in the sector either die or fall ill by the time they reach 65.
They claim that in many cases they cannot keep working until retirement because of the demands of the job.
More than 10,000 construction workers demonstrated in March in the Swiss capital, Bern, and threatened a national strike on April 3 if their demands were not met.
A last-minute deal with the SCF appeared to have resolved the dispute.
But construction unions claim that employers have since failed to keep their side of the bargain. Employers have denied they reneged on the deal.
According to Pedrina, the last strike by construction workers in Switzerland took place in 1947 following a dispute over pay and working times.
The last general strike took place in 1918. More recently, tensions surfaced periodically during the 1980s and early 1990s.
Compared with its European neighbours, strikes are rare in Switzerland due to a long tradition of avoiding industrial conflict through negotiation.
A peace accord signed in 1937 in the engineering and watchmaking industries has provided a foundation for consensus bargaining between unions and employers.
This has helped to ensure more than 50 years of relatively peaceful labour relations.
Under the accord's terms, both sides in a dispute must undergo arbitration or risk substantial fines.
The strike comes amid a period of simmering industrial unrest in Switzerland.
Swiss postal workers have also threatened to strike against plans to shed 2,500 jobs around the country.
On Friday several thousand public sector employees took to the streets of Bern in protest against planned cantonal spending cuts.
November 1918: troops put down the only general strike in Switzerland's history.
July 1937: an accord within the watchmaking and engineering industries helps ensure 50 years of relative industrial peace.
1945-46: Switzerland experiences a record number of strikes.
The industry employs around 90,000 workers.