Determined Mel Gibson is taking on some of Hollywood’s biggest stars in a monumental political battle.

The outspoken actor has a new passion–challenging Brad Pitt, Michael J. Fox and the legacy of Christopher Reeve in a struggle over government funding for embryonic stem-cell research.

The “Braveheart” star went to war against a proposition on California’s November 2 ballot–asking the state’s taxpayers to approve a $3 billion bond to fund stem-cell research.

Mel, a devout Roman Catholic, is against recovering stem cells from embryos.

Brad, Michael and other big names supported the proposal. “And Christopher Reeve fought for the funding of stem-cell research until his dying breath,” said a source.

“But Mel is not one to shy away from controversy. Because of his religious convictions, he opposed the bond.”

The “Passion of the Christ” director was so committed to shooting down “Prop 71,” he even went on “Good Morning America” to tackle the issue.

Brad Pitt also weighed in, telling “Today” that he backs government funding of stem-cell research.

“Brad is furiou

s because he thinks Mel is insensitive to Christopher Reeve’s memory and to Michael J. Fox, who is fighting a valiant battle with Parkinson’s disease,” said an insider.

“It’s a bold move on Mel’s part. “Hollywood power brokers have always tended to see eye-to-eye on political matters, but in the past few years Hollywood has splintered.

“Mel is not afraid to take on the powers that be.”

The stem-cell feud shows no signs of stopping.

“There is a lot at stake over this fight,” said the source.

“Mel truly believes in what he’s preaching, but fighting the entertainment establishment has always been a dicey proposition.

“This is Round One in what promises to be one of Hollywood’s fiercest battles. We haven’t heard the last from any of these stars.”