Having to make cuts of £380m to the NHS in Wales by April 2011 will be the biggest challenge for the country's service in years, according to managers.
Research carried out by BBC Wales shows staff have already had pay cuts imposed, and patients had services reduced.
The looming government spending review, due out on 20 October, threatens even bigger cuts.
Many Welsh health boards and trusts are already enacting "rigorous vacancy controls" as a way of cutting staff.
BBC Wales said one health board document points out that a growing gap between patients' expectations and what the NHS can actually provide will increase tension.
Betsi Cadwaladr University Health Board, the largest in Wales, has a £1bn annual budget but has been told it needs to cut around £70m from this in 2010-11 alone.
The board's vice-chair, Lyndon Miles, said: "I wouldn't pretend that it's easy but there are opportunities. We are looking at lots of areas. We are looking at the way we spend at the moment, for example employing locums and agency staff and the way we recruit."
Cutting staff costs is a common theme for the country's seven health boards and three NHS trusts. Betsi Cadwaladr said it plans to slash £14m from its wage bill in 2010-11 and is proposing the closure of HM Stanley Hospital in Denbighshire.
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