Health workers have a non-negotiable right to exercise conscientious objection by refusing to participate in an abortion, Pope Francis said on Thursday, calling the procedure "murder".It was at least the third time in a month that the pope has spoken out strongly against abortion, which has become a major political issue in a number of countries, including the United States.Last week a U.S. appeals court temporarily reinstated Texas's restrictive abortion law, which bars the procedure as early as six weeks into pregnancy and outsources enforcement of the ban to ordinary citizens."Today it has become a bit fashionable to think that maybe it would be good to do away with conscientious objection (in the medical field)," he said to participants of a conference in Rome of hospital pharmacists."It (conscientious objection) should never be negotiated, it is the ultimate responsibility of heath professionals," he said, adding that it was particularly applicable to abortion."Know that on this I am very clear: It is murder and it is never licit to be an accomplice," he said.Most countries have laws that provide for some form of conscientious objection by health professionals, but abortion rights activists say not all are fulfilling their duty to refer a woman to another doctor.In some Scandinavian countries, doctors are barred from refusing to provide any medical care that is legal.Last month, Francis told reporters on the plane returning from Slovakia that abortion was "murder", even soon after conception, but appeared to criticise some U.S. Catholic bishops for dealing with U.S. President Joe Biden's pro-choice position in a political rather than pastoral way.The Roman Catholic Church teaches that life begins at the moment of conception.In June a divided conference of U.S. Roman Catholic bishops voted to draft a statement on communion that may admonish Catholic politicians, including Biden. They are due to take up the issue again next month.