Flynn offered praise for the likely Republican presidential candidate Donald Trump.
Donald Trump is formally vetting a retired general as a potential running mate, but the 33-year Army veteran's views on social issues are sure to draw an outcry from Republicans already wary about Trump's conservative credentials.
Trump is expected to make a decision this week before the Republican National Convention begins in Cleveland on Monday.
"His pro-abortion position is unacceptable and would undermine the pro-life policy commitments that Mr. Trump has made throughout the campaign", Dannenfelser said in a statement.
"Retired Army Lt. Gen. Michael Flynn, already a top adviser on national security to Donald Trump, might soon find himself receiving a major promotion".
Flynn, a registered Democrat but a fierce critic of President Barack Obama, previously ran the Defense Intelligence Agency.
Abortion-rights supporters were skeptical that any ticket headed by Trump would be open to their positions.
Trump has appeared most recently with New Jersey Governor Chris Christie, but has also campaigned with House of Representatives Speaker Newt Gingrich.
"I never met with him once", Flynn told the Daily Caller. He later served as NATO's director of military intelligence and finally head of the Defense Intelligence Agency.
Of all the issues that make Americans fear a Trump presidency, the fact that he would have access to the nuclear codes is probably the most dominant concern, which is why it makes some sense if he were to nominate someone from the military. "I have provided advice for quite some time now to him, and I would tell you he's a great listener, he asks great questions and he's somebody that has a vision for this country that I think we need right now, we desperately need". "It's wonderful", Flynn said.
According to his bio, Flynn served as the director of intelligence, Joint Staff from July, 2008 to June, 2009, then the director of intelligence, International Security Assistance Force in Afghanistan from June 2009 to October 2010.
He said that Clinton spearheaded a failed plan to improve relations between Russian President Vladimir Putin and Obama. Christie was picked by almost a tenth of Trump supporters.