Americans are deeply divided over the bill

On Wednesday President George W Bush is expected to sign the bill, passed by Congress in October, which would outlaw a procedure known as partial-birth abortion used in the later stages of pregnancy.

The groups filed suits in New York, San Francisco and the Mid-West state of Nebraska, saying they were determined to intervene to halt what they called a dangerous law.

We have to take every step we can to intervene before this dangerous bill becomes a law Gloria Feldt Planned Parenthood Federation of America

Partial-birth abortion, which is already outlawed in a number of US states, involves the foetus being partially delivered before it is killed by piercing its skull and removing the brain.

But pro-abortionists say the bill is so open-ended it could affect more than one type of abortion, and is unconstitutional because it lacks an exception for cases where the woman's health is at risk.

""We have to take every step we can to intervene before this dangerous bill becomes a law," Gloria Feldt, president of a family planning group which filed the San Francisco case, told the New York Times newspaper.

"We may have only hours to spare when [the president] actually signs it, and we just can't take the risk that our doctors and patients can be uncovered."

Supporters of the bill say that partial-birth abortion procedure is never necessary to protect the health of the mother.