"The health-care service that's at issue here is contraception, which means prior to conception," Casey said.
But abortion has been a central part of the Hobby Lobby firestorm, which has also touched on health care, religious freedom, individual rights, and election-year politics.
Casey on Tuesday became the first antiabortion Democrat to cosponsor the bill, aimed at reversing the Supreme Court decision allowing business owners to exclude certain contraception options from their employee health packages. Some business owners said certain types of contraception could amount to abortion, an idea disputed by many doctors and scientists.
"I'm a pro-life Democrat, always have been, always will be," Casey said. He later added: "I'll go with the scientists on what contraception is, rather than a religious viewpoint of what science is."
He also worried about private executives using their religious beliefs to restrict access to other types of health coverage.
Even with Casey's support, the bill has little chance of becoming law, but Democrats see it as an opportunity to highlight their support for women's rights.
Democratic leaders expect a key procedural vote Wednesday, but the measure faces opposition from Republicans and some Democrats from conservative states. It has virtually no hope of clearing the GOP-controlled House.
Casey joined 44 other Democrats sponsoring or cosponsoring the bill.
Conservative critics have often said his voting record has undermined his antiabortion credentials. "His reputation as a conservative is different than the reality of the stances that he takes," said Randall Wenger, chief counsel of the Pennsylvania Family Institute.
Wenger called Casey's support of the bill "disappointing" because "government should never be in the position of forcing someone to violate their most deeply held convictions."
For Casey, his position represents a third recent stand with his party's left on a cultural fight in the national spotlight.
In December 2012, he reversed his long-held opposition to new gun laws after the Sandy Hook School shootings. Less than four months later he joined the many Democrats who changed course to embrace same-sex marriage.
In hoping to overturn the so-called Hobby Lobby ruling, though, Casey said there had been no change in his views.
"This is entirely consistent with my votes," he said, pointing to previous support of contraception.
He also stressed that there were still protections in place for religious nonprofits, such as hospitals or private schools, but said those safeguards shouldn't apply to for-profit businesses.
The abortion debate has a long association with Casey's family. His late father, former Pa. Gov. Robert P. Casey, was an antiabortion Democrat who clashed with national party leaders over the issue.
The younger Casey has tried to find a balance between his party's pro-abortion rights orthodoxy and his antiabortion stand, said Christopher Borick, a political scientist at Muhlenberg College.
"He has remained a pro-life Democrat but one who has stretched the bounds of that definition," Borick said. "On issues like contraception, he's clearly been much more in line with the approach of the Democratic Party position and not those of the teachings of the Catholic Church."
In the Supreme Court case - revolving around Hobby Lobby, a chain founded in Oklahoma City, and the Lancaster County-based Conestoga Woods Specialties - business owners raised religious objections to some types of contraception coverage that President Obama's health-care law mandated as part of employee health insurance. They argued that certain methods amounted to abortion.
The court ruled 5-4 for the businesses, drawing praise from Republicans and scorn from Democrats.
"Religious liberty belongs to all of us; it does not belong to a corporation," Sen. Cory A. Booker (D., N.J.) said on the Senate floor Tuesday morning. "Religious liberty means being free from having other people's religions foisted upon you."
In a statement on the day of the June 30 ruling, Sen. Pat Toomey (R., Pa.) called it "a win for religious liberty."
He has cosponsored a bill aimed at providing a religious exemption to the health law requirement on contraceptives.