"It instead opted to use statutory language that pushed almost every boundary that the Supreme Court has imposed for these types of laws," the judges said.
Previous attempts by Michigan lawmakers to stop the procedure were struck down by federal courts in 1997 and 2001.
The U.S. Supreme Court in April upheld the federal Partial-Birth Abortion Ban Act, with the majority opinion carefully distinguishing the controversial procedure from a more common abortion method used in the second trimester of pregnancy. The latter was unaffected by the ruling.
The appeals panel affirmed a Detroit district judge's opinion that the 2004 Legal Birth Definition Act in Michigan places an "undue burden" on a woman's right to have an abortion.
Abortion rights groups have said the law - unlike the federal ban and the law in Ohio - overreached and would have banned pre-viable abortions, including the most common method of second-trimester abortion. The appeals court agreed.
"The Michigan statute contains no similar exception or clear definitions that would avoid sweeping up protected abortion procedures within its prohibition," the court wrote.
The Michigan Legislature approved the abortion law in June 2004. Hundreds of thousands of voters signed petitions that allowed the bill to become law with only the approval of the House and Senate - both of which were controlled by Republicans at the time - after Democratic Gov. Jennifer Granholm vetoed it.
