At her family's Passover seder last April, Rabbi Debra Orenstein opted for the layered look: an ordinary T-shirt topped by a purple-and-black blouse made in India - and very likely sewn in a sweatshop by slave labor.

At the moment when the seder's leader typically holds up a piece of matzo and declares, "This is the bread of affliction" - symbolizing the ancient Israelites' enslavement and hasty flight from Egypt - Orenstein startled her guests by peeling off the Indian blouse. "This," she announced, "is the shirt of affliction!"

Passover begins Friday evening; more than 90 percent of Jews around the world will mark the holiday with seders: ritual dinners of family and friends accompanied by songs, prayers, and readings that tell the Biblical story of Exodus.

Some will use the seder as a frame to discuss immigration or feminism, the inclusion of LGBTQ people or the mass incarceration of African Americans. They will talk about their own "enslavement" to social media or oppressive work schedules. They will chant, "Now we are slaves; next year may we be free."

Orenstein and other Jewish leaders want people to know those words are not merely a metaphor.

Working with Free the Slaves, a Washington advocacy center, Orenstein, rabbi of Congregation B'nai Israel in Emerson, N.J., created the Passover Project, a just-released set of resources - songs, readings, stories, quotes, and activities - to boost awareness and spark action to end human trafficking and enslavement.

"If Jews are ever going to talk about ending slavery, this is the season when they'll do it - a time when people are thinking about questions of freedom," she says. "The message of Passover is one of empathy."

According to Free the Slaves, which was launched in 2000 to liberate slaves and alter the conditions that allow slavery to persist, between 21 million and 36 million enslaved people toil across the world today. They peel shrimp in Thailand, harvest cacao in West Africa, perform sex work under coercion and threat. Twenty-six percent of them are children.

Orenstein didn't grasp the extent of modern slavery until a few years ago, when she agreed to write a sermon on the topic. She scoured websites and pored over books, including one whose author recounted entering a brothel in South Asia and being offered a young woman with Down syndrome "for an amount of money so low it was frightening," Orenstein recalls.

What she learned transfigured her. "The minute I was faced with what we are still allowing to happen in the world, I felt I couldn't rest." A conversation with Free the Slaves executive director Maurice Middleberg eventually grew into the Passover Project.

Though the resources, available at FreeTheSlaves.net/Judaism, have been out for just a few months, area synagogues are starting to embrace them.

Rabbi David Ackerman of Beth Am Israel in Penn Valley is making material from Free the Slaves available at weekly Shabbat services, and he raised the issue of modern slavery with the high school group he leads on Monday nights. "We've got this big festival of freedom coming up," he reminded the teens. "Can you celebrate our freedom knowing that other people don't share in that?"

At Temple Beth Hillel-Beth El in Wynnewood, Rabbi Neil Cooper will funnel some of his congregation's pre-Passover tzedakah collection of money to Free the Slaves. And for Rabbi Eli Freedman, a leader of Congregation Rodeph Shalom on North Broad Street, Passover offers a rich opportunity to infuse the Biblical narrative with contemporary relevance. "It's one thing just to say to someone, 'Slavery's bad.' But when we tell a story, it has a lasting impact."

That's why Orenstein is urging her congregants to watch a four-minute video, "Building Freedom Brick by Brick," about formerly enslaved brick-makers in India. It's why Middleberg plans to put a padlock on his family's seder plate alongside the traditional shank bone and bitter herbs. It's why Glenside rabbi and educator Erin Hirsh will bypass the store-bought chocolate-covered matzo and instead dip her own in fair-trade chocolate, then explain the choice to her nieces and nephews.

"I think many people bring women's issues or environmental issues into the seder," says Gabrielle Kaplan-Mayer, a writer and educator at Mishkan Shalom, a Reconstructionist synagogue in Roxborough. "But this feels different. Slavery is the actual theme of the seder. This is much more of a literal connection."

On a recent Wednesday night, Kaplan-Mayer gathered nine teenage members of Mishkan's Food for Thought class, a monthly session to experience Jewish culture and tradition through cooking.

"Do you guys know a little bit about the particular issue of chocolate?" she asked.

Gina Golden, 15, nodded: "People who grow the cocoa don't get paid as much as the companies who make the chocolate . . . they're not giving them enough money to live."

"The reality is that children are out there farming cocoa instead of being at school," Kaplan-Mayer said. "What's it going to take to change the way these corporations work?"

She held up a 2.8-ounce bar of Equal Exchange organic milk chocolate. "Know how much this was?"

"Eight dollars?" guessed Eli Rossman, 16.

"Not that bad. $3.99," Kaplan-Mayer said, noting that she shopped at the CreekSide Food Co-op in Elkins Park, after discovering there was no free-trade chocolate at her local Acme. "It's really cool that everyone who was involved in farming the cocoa for this chocolate was paid a fair wage."

"Is there any lobbying for different regulations, to make change through legislation?" asked 16-year-old Anna Luce.

Kaplan-Mayer said Free the Slaves and other organizations were doing just that; she promised to send Luce some information after the class. But, first, the sweet task at hand: making several batches of chocolate-covered almond matzo toffee.

"We call it 'matzo crack,' " Luce said. "It's so wicked. You will become addicted."

"Addicted to fair-trade chocolate?" Kaplan-Mayer said. "That's OK!"

Creators of the Passover Project hope heightened awareness of modern slavery will persist beyond the eight-day holiday. The project includes a year-round curriculum with lessons for all age groups. Free the Slaves wants to enlist 180 synagogues, Jewish schools, and organizations as partners in the effort to end slavery.

For Middleberg, the issue has personal impact: His wife is the descendant of abolitionists, and his grandfather was a slave-laborer in Auschwitz, repairing watches stolen by Nazi soldiers.

"The resonance [of slavery] is so powerful, so immediate for Jewish communities," he says. "So what happens when Pesach is over? This is an enduring responsibility. It goes on all year."