British Airways has said 800 workers have volunteered to work for nothing for up to a month, following the airline's request to cut costs.
Another 4,000 employees are taking unpaid leave, while 1,400 people have volunteered to work part-time.
The airline had put the proposal to 40,000 staff. BA chief Willie Walsh has already agreed to work unpaid in July, forgoing his month's salary of £61,000.
Unions said asking staff to work for nothing was "unrealistic".
The airline, which is struggling in the downturn, says the move will save £10m.
Many firms across different industries have been reducing their workforces and cutting workers' hours in a bid to save costs during the economic downturn.
"What makes BA stand out is that it is asking workers to work for nothing for a period, rather than simply reducing pay through fewer hours," said Jane Amphlett, an employment lawyer with Finers Stephens Innocent.
In May, BA reported a record annual loss of £401m, stemming partly from higher fuel bills and other costs.
Anonymous BA worker: Working without pay "laughable"
Following the response from workers, Mr Walsh said: "This is a fantastic first response. I want to thank everyone who has volunteered to help us pull through this difficult period."
He added: "This response clearly shows the significant difference individuals can make."
Mr Walsh said staff could volunteer for the programme later in the year too.
But the union Unite said that while it supported the current BA scheme which encourages part-time working, unpaid leave, and career breaks, it did not support this proposal.
"The proposal for employees to 'work for nothing' is unrealistic," said Unite national officer Brian Boyd.
"The fact that less than 2% of BA's workforce chose to take up this option demonstrates that there is no real support for this."
Starting in July, the 800 workers have the chance to stagger the days worked unpaid over a period of up to six months, with the pay deduction spread over three or six months.
Those volunteering to work part-time can do so for a period of between one month and one year, before another review is expected later in 2009.
Similarly those on unpaid leave can take the time off for up to a year.
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