UPDATE, 7:53a: More from the Associated Press:
But Stupak tells the AP the attacks didn't influence his decision and he could win re-election if he tried.
He plans to announce his decision at a 12:30 p.m. news conference at Northern MI University in Marquette....
He says he wants to spend more time with his family and start a new career after 18 years in Congress.
7:46a: From CBS News this morning:
MI Rep. Bart Stupak, the congressman who led anti-abortion rights Democrats in the House during health care negotiations, will retire this year, CBS News has learned. He is expected to announce his plans later this morning....
Had Stupak sought re-election, he would have faced challengers from both the left and the right backed by interest groups angered by Stupak's health care vote.
Stupak negotiated with Democratic leaders down to the 11th hour for stricter abortion language in the health care bill, but he ultimately voted for it after President Obama agreed to sign an executive order assuring the new laws will keep taxpayer dollars from funding abortions.
That prompted the conservative Tea Party Express to launch a $250k ad campaign against Stupak this week. The group also scheduled a handful of stops on its bus tour in Stupak's district.
On the left, the abortion rights group NARAL Pro-Choice America has been working to defeat Stupak and instead elect his Democratic primary challenger Connie Saltonstall.
On one hand my anger at Stupak is heightened by this announcement. He created this huge mess and now is walking away. I smell chicken. On the other hand, I feel a sense of vindication.
I expect Stupak will play the martyr when he makes his statement.
I also expect Stupak's announcement will put the fear of God into the other 19 pro-life Democrat turncoats.