President George W. Bush vetoed legislation yesterday that would expand federally funded embryonic stem cell research.
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. He announced no new funding.
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.
The president and other critics condemn the legislation as morally offensive because it would lead to the 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," Mr Bush said. "I will not allow our nation to cross this moral line."
Embryonic stem cells are the source of every cell, tissue and organ in the body. Scientists study them to understand the biology not only of disease, but of life itself, and want to use them to find cures for illness such as Parkinson's, cancer and diabetes.
Polls show the stem-cell bill is backed by more than 60 per cent of American voters.
"Once again, the president has ignored the will of the American people, of leading medical researchers, and of a bipartisan majority of the Congress," said House Speaker Nancy Pelosi, a California Democrat.