text: The boards are forecast to over spend by £146m this year.
  In one case - Abertawe Bro Morgannwg University Health Board (ABMU) - the financial outlook is said to be "extremely challenging".
  The health board, which covers Swansea and Bridgend, said it was attempting to cut agency staff costs.
  As well as ABMU there are overspends at Betsi Cadwaladr in north Wales, Cardiff and Vale board and Hywel Dda in mid and west Wales.
  Betsi Cadwaladr's deficit is now forecast to be £30m, Hywel Dda £49.9m, ABMU £35m and Cardiff and Vale £31m for the 2016-17 financial year.
  The health boards will not face a bill to repay the money, but they will be expected to balance their books in the next financial year.
  In the previous year, Betsi Cadwaladr and Hywel Dda had a combined deficit of £50m while Cardiff and Vale and ABMU both broke even.
  Betsi Cadwaladr has been under direct control of the Welsh Government since June 2015.
  The other three boards were placed under an increased level of scrutiny from ministers last September due to doubts about their ability to tackle the financial challenges they face.
  Health Secretary Vaughan Gething told BBC Radio's Good Morning Wales programme he was "pretty certain" services would not be cut "simply because of money".
  "We'll change services but that's because we should change some of our services, because they currently don't deliver the right value and the best quality," he added.
  He said the health service had a responsibility to provide "high-quality care" and at the same time "to do more to live within its means".
  A Welsh Government spokeswoman said: "The position in these four health boards is unacceptable, and we have made it clear that we expect them to take action to significantly improve their financial position."
  She said ministers will not approve financial plans "that do not deliver such improvements".
  "Individual organisations that exceed their allocated resources, have not - and will not - be bailed out," she said, adding that the government is "working alongside all organisations to improve their respective positions" and that the "overall health budget will be balanced for the 2016-17 financial year".
  ABMU has gone from a break-even position to a forecast deficit of £39m this year, and another forecast deficit of £53m next year.
  The health board has average running costs of £3m a day, so a £39m deficit is equivalent to the cost of running the board for 13 days.
  It said it was focusing on an intensive recruitment drive to cut down on the cost of agency staff, as well as reducing waste in prescription medication.
  A spokeswoman said: "There are many challenges facing us when trying to identify savings that won't compromise patient safety and quality of care, at the same time as demand on our services increases."
  A spokesman for the Betsi Cadwaladr University Health Board said: "We have worked hard throughout the year, and worked closely with Welsh Government, to address our challenges, and we will continue to do so going forward."
  Stephen Foster, of Hywel Dda University Health Board, said: "This is not the financial situation that we would want to find ourselves in and we are putting together significant plans to turn it around."
  Analysis by BBC Wales political editor Nick Servini
  These figures show a dramatic deterioration in the finances of four out of Wales' seven health boards.
  They have also prompted a hard-hitting response from the Welsh Government which, until this point, has been keen to stress how they approach problems together.
  The tone resembles the approach of the man in charge of the English NHS, Jeremy Hunt, who has not been afraid of calling out heath trusts he believes are under-performing.
  The Welsh Government has called for a significant improvement in the financial performance.
  That will be easier said than done in the face of intense pressure on these organisations.
  More from Nick
target: Four health boards which are due to see their overall budget deficits triple in size will not be bailed out, the Welsh Government has said.