Sister Simone Campbell says she is on a mission to protect the poor—from Rep. Paul Ryan.

This summer, the outspoken Catholic nun led a bus tour across the country called “Nuns on the Bus,” protesting the Wisconsin congressman’s proposed federal budget plan, which she says would slash funds for social programs for low-income people. Now she is recruiting teams of sisters to lobby their state legislators to insist on protections for the poor, such as an expansion of Medicaid. She has invited Ryan and Mitt Romney to join her in spending a day with poor people. She even took on conservative pundit Bill O’Reilly on Fox News this week to make her point.

“That was kind of wild,” she says of the O’Reilly show, which resulted in an on-air fight. “You have to think of it as missionary activity,” she laughs. On the show, O’Reilly argued that the poverty rate had gone up under President Obama, so the current system isn’t working. “Tell me what you want, Sister,” he demanded. Her reply: “What I want is money in the pockets of hardworking people who are living below the poverty level…The Ryan budget gives money to the top, not the bottom.”

Sister Simone is the executive director of a Catholic advocacy group in Washington, D.C., called Network, which lobbies Congress for policies that help the poor. She and her fellow sisters have zeroed in on the newly chosen vice-presidential candidate because he proposes reducing the federal budget deficit through substantial cuts in spending, which Sister Simone believes would hit low-income people hard. “In order to do what he says he is going to do, it takes drastic cuts,” she says, adding that Ryan does not generally go into detail about the specific programs for the poor that would be affected. “He’s trying to avoid enumerating them,” she says. “The truth is, there’s a shift of money to the top—tax cuts for the wealthy.” Representatives for Ryan didn’t immediately respond to a request for comment.

Sister Simone says she met with Ryan personally in July, after her bus tour. “We agreed that we would say we had a cordial conversation,” she says of the half-hour meeting. “We agreed to disagree. Actually, we both agreed that we care passionately about the future of this country. So we did find some common ground.”

She says her bus tour, which covered nine states in two weeks, fired her up. “The more we were on the road, the more impassioned we became,” she says. “We saw all these low-income communities, all the people who would be affected. By the end, we were fairly nuts about it.”

She describes visiting unique social programs aided by federal funds, such as a housing project near Pittsburgh that also helps people craft résumés. In Detroit, she says, an adult literacy program made an interesting discovery: one-on-one training doesn’t work as well as when one teacher instructs three students. “People are more committed that way,” she says. “If one person doesn’t show up, they call each other.” In Toledo, a center focuses on kids who get suspended from school, going home to meet their families. It was discovered that a pair of 10-year-old twins, always in trouble for fighting, were living with a single mother, bedridden with multiple sclerosis. Now she is getting help.

“Ryan thinks churches can pick up the tab,” Sister Simone says. “That’s ridiculous. The magnitude of the need is so great.”

Ryan, who is a Catholic himself, argues that his budget plan is in line with church teachings. He says the poor should not be kept poor and overly dependent on the government. He says some people take advantage of welfare programs, ultimately hurting those most in need, and that the budget deficit has ballooned out of control, so spending needs to be curtailed and refocused.

Sister Simone says it’s not the social programs that are keeping people poor, but rather the economy. “The problem is not enough jobs and low wages,” she says, adding: “Catholic teaching is based on solidarity. Ryan doesn’t understand that all decisions need to be made with the common good in mind.”

Asked if she anticipated that Ryan would be Romney’s pick for vice president, she says: “Heavens, no. He’s not from a state that’s an important swing state. I don’t see what he brings to the ticket. He thinks seniors are getting too big of a free ride. I don’t understand it.”

The nuns aren’t the only Catholics making noise. A pair of high-profile bishops—Bishop Stephen E. Blaire and Bishop Richard E. Pates—have been sending letters to Congress about the importance of protections for the poor, speaking on behalf of the Conference of Catholic Bishops. “The bishops have said Ryan’s budget doesn’t pass the moral test,” Sister Simone says, “and we stand with the bishops on that one.”

Catholic sisters have had a busy year. Recently the Vatican cracked down on the church’s main umbrella group of U.S. nuns, called the Leadership Conference of Women Religious, or the LCWR, saying the nuns were showing signs of “radical feminism” for not vigorously promoting church teachings on issues such as homosexuality and abortion. The nuns fought back, calling the Vatican move polarizing. Last week, the sisters met with a bishop who has been appointed to oversee them, expressing their concerns.

Sister Simone describes her group, Network, as a “friend” of the LCWR, noting that her group has no formal connection to the Vatican. She notes, however, that the Vatican called Network a “problem” in its recent assessment of American sisters. She believes that’s because her group supports the Affordable Care Act. During the 2010 congressional debate over health-care reform, Sister Simone galvanized nuns to sign a letter to Congress in support of the act. Vatican officials “think federal funding is going to abortion” under the act, she says. “It isn’t. Community clinics cannot use federal funds for abortion.”

A California native, Sister Simone was born in 1945, entered the convent in 1964, and took her vows in 1967. She has been the executive director of Network since 2004. Before that, she was the executive director of Jericho, a California public-policy organization that works to protect people living in poverty. Prior to that, she founded and served as the lead attorney for the Community Law Center in Oakland, Calif., where she also worked with the poor.

As for her invitation to Ryan and Romney to come spend a day with the poor, she says, she’s waiting for a reply.