President George W Bush today vetoed legislation to expand federally funded embryonic stem cell research, triggering an uphill battle in the Democratic-led Congress to override him.
Two-thirds majority votes would be needed in the Senate and House of Representatives to overcome Mr Bush's opposition and make the bill law, and backers conceded they are short of support.
In addition to vetoing such legislation for the second time in two years, Mr Bush issued an executive order to encourage scientists to work with the federal government to derive new methods to obtain stem cells without harming human embryos.
Critics called the presidential order a sham and said he should have signed into law the stem-cell bill, which polls show is backed by more than 60 per cent of American voters who see the measure as a way combat a host of illnesses.
"President Bush isn't fooling anyone with this executive order; and the fact that it doesn't change the policy adds insult to injury for the millions of patients who suffer every day," said Sean Tipton of the Coalition for the Advancement of Medical
Research, a nonpartisan advocacy group that represents more than 100 patient and scientific organizations.
The president and other critics condemn the legislation as morally offensive because it would lead to destruction of human embryos to derive stem cells.
"If this legislation became law, it would compel American taxpayers -- for the first time in our history -- to support the deliberate destruction of human embryos," the White House said. "The president has made it clear ... that he will not allow the nation to cross this moral line."
Backers note the legislation would only permit scientists to use embryos left over from fertility treatments that would otherwise be discarded. They also say it could clear the way for possible medical breakthroughs that could help millions of people suffering with debilitating diseases.