HIV positive Chileans, Mexicans and Dominicans were among the more than 100,000 people who crossed the Brooklyn Bridge last week to protest the controversial new immigration bill working its way through Congress. “This bill will drive HIV positive undocumented immigrants further underground,” warned Jose Cruz, a staffer at the New York AIDS group Housing Works who made the Monday afternoon march with a banner reading, “The AIDS Crisis Isn’t Over Until We Care for All Immigrants.”

HIV is a top concern for many of the protesters so far clogging 140 U.S. cities to call for a softening of the proposals now on the table in Washington. The version of the bill that passed the House of Representatives in December (and will need to synch up with a version now under discussion in the Senate) would make just being an undocumented immigrant a felony—and prevent agencies from providing food, housing or health care. HIV advocates say positive immigrants would be especially vulnerable.

Also under that version, detention would be mandatory, with immigrants staying behind bars for months or years before seeing a judge, likely without adequate access to health care. “Positive immigrants do not get appropriate medical care,” asserts Sarah Sohn of Immigration Equality, a rights group, “and they face discrimination by [corrections] officers.”

One persistent fear is that HIV positive undocumented immigrants may lose the help they get paying for HIV meds through AIDS Drug Assistance Programs (ADAP). “It’s hard to describe the impact of something so catastrophic,” says Dennis de Leon of the New York-based Latino Commission on AIDS, “except to say that [such a law would] jeopardize the lives of people with HIV.”

Finding HIV care and services is already tricky for undocumented immigrants. Most learn to subsist below government radar for fear of being sent home to countries where there may be no HIV care at all and where some face discrimination for their HIV status or sexuality. And you can’t get Medicare or nonemergency hospitalization without a Green Card.

What’s to come? Cruz believes that lawmakers in Washington will be so moved by this month’s unprecedented turnout of serious, hard-working immigrants that they will pass something kinder than the House version—perhaps closer to the current Senate version, for instance, which drops the felony clause. “In this country, people believe in fairness and justice,” he says. “You can’t argue with a mother who toils and pays taxes.”

Sohn is less optimistic, and de Leon hesitates to make a prediction. What he will commit, however, is that whatever happens in Washington, the services of the Latino Commission won’t change. “We will continue to serve immigrants without regard to legal status,” he says. An ever-widening circle of groups have made the same promise.