Regi stered nurses at Providence Hospital voted to unionize Tuesday, continuing a wave of organizing among D.C. nurses as health-care industry uncertainties trickle down to rank-and-file employees.

Providence becomes the seventh D.C. hospital with nurses organized under the banner of National Nurses United, a federation of nurses unions. Organizers hope that bringing Providence’s roughly 400 RNs into the fold will help D.C. Council legislation that would mandate certain nurse staffing levels in city hospitals. That legislation is languishing amid fierce lobbying by hospital officials, who contend that “staffing ratios” increase costs without improving patient care.

Carl Ginsburg, a spokesman for National Nurses United, said he expected the staffing bill to get “greater consideration” from lawmakers in light of the union vote, which was 232 to 66. “Nurses from Providence have already testified about staffing shortcomings, pronounced staffing shortcomings” jeopardizing patient care, he said. “They have been forthright in their demand that a new safe staffing law be passed in the District.”

But several key D.C. Council members are opposed to the bill — including, crucially, Yvette M. Alexander, who chairs the Health Committee — and there is little immediate prospect of its becoming law.

NNU-organized nurses have had contentious contract negotiations, particularly at MedStar Washington Hospital Center, the city’s largest acute-care hospital, where nurses conducted a brief walkout in 2011. Meanwhile, at Providence, one of the District’s smallest acute-care hospitals, a top executive said she was hopeful the organizing effort will have little outward effect. “We’ll continue to serve our community and serve all of our patients, with special attention to those who are poor or vulnerable,” said Senior Vice President Karol Marciano. “There will be no change to any of our strategic plans.”

Marciano also said there will be no significant changes to the hospital’s staffing model. But she said she understood the impulses behind the organizing effort. “I think it has everything to do with the challenges we’re facing these days. . . . All of health care and the delivery aspects of health care are changing,” she said. “Those changes can drive changes in the way you structure your workforce.”