The early retirement scheme, introduced a dozen years ago, is considered one of Switzerland’s signal social successes but is in danger because of a shortfall in contributions, the Blick newspaper reported online on Monday.

Since 2003, more than than 13,000 construction workers have taken advantage of the plan by taking their pensions from the age of 60, the newspaper said.

But the influx of baby boomers retiring means the plan needs extra funds to avoid going in the red starting next year.

Unions complain that construction companies are not acting to deal with this “urgent situation”.

Construction workers currently receive 65 percent of the basic salary plus 500 francs, which amounts to about 4,500 francs a month for a mason, Blick said.

But without extra funding the pensions will either be cut by 800 francs a month or the retirement age will be increased.

A representative from construction industry employers downplayed the concerns.

“The funding is a technical issue,” Martin A. Senn, head of policy at the Swiss Contractors’ Association, told Blick.

“We shall find a solution,” Senn said.

“Retirement from 60 should be possible in the future.”

Construction workers campaigned for early retirement with a massive demonstration in Bern in 2002.

Unions representing the workers have argued that because of the physical risks of the trade many of them cannot continue working until the normal retirement age (for men) of 65.

Statistics showed that more than 40 percent of Swiss construction workers either fall ill or die prematurely by the time they reach 65 because of the demands of their job.