Jeanne Batalova, a policy analyst with the Migration Policy Institute, said there are fine distinctions over what the term means among the states and local governments that have adopted complex policies on how to deal with illegal immigrants.
"The term (sanctuary city) is used liberally," she said. "There is no one consistent definition."
Romney charged again during Wednesday's GOP debate in Florida that Giuliani ran a "sanctuary city" while mayor of New York City because he did not turn in to federal authorities all of the illegal immigrants who used city services or broke laws. Giuliani countered that Romney allowed six sanctuary cities while governor of Massachusetts, and even ran a "sanctuary mansion" because he employed illegal immigrants as landscapers.
A 2005 Congressional Research Service report described 32 cities or counties — including New York — that adopted sanctuary policies in which their employees were not required to report illegal immigrants to federal authorities.
Giuliani said "a lot of criminals would have gone free" if not for key information illegal immigrants provided police.
Giuliani said exceptions were made in New York so illegal immigrants could receive emergency medical care and send their children to schools, both of which are requirements of federal law.
The congressional report also said the cities of Orleans and Cambridge in Massachusetts have "sanctuary policies." Giuliani spokeswoman Jennifer Mastin produced a list Thursday of others with similar policies, including Somerville, Brookline, Brewster and Lexington. Romney has not disputed there were sanctuary cities in the Bay State.
On the point about Romney running a "sanctuary mansion," there is no governor's mansion in Massachusetts. The Boston Globe reported last year that Romney employed a landscaping company at his home in Belmont that used non-citizens from Guatemala. Romney has said he did not know about the company's hiring policies.
At the debate, Romney said it was "offensive" that Giuliani seemed to suggest "if you hear someone with a funny accent, you, as a homeowner, are supposed to go out there and say, 'I want to see your papers?' "
The sparring over illegal immigration between Romney and Giuliani comes at a critical time in the campaign, just about a month before voters start picking presidential nominees. In Iowa, Romney is essentially tied with former Arkansas governor Mike Huckabee in state polls. Giuliani is trying to make a major push in New Hampshire, where Romney has the lead in state polls.
Romney also charged at Wednesday's debate that Huckabee proposed allowing children of illegal immigrants to seek grants under an Arkansas scholarship program. The proposal was not adopted by the Arkansas state legislature.
"We are a better country than to punish children for what their parents did," Huckabee said Wednesday.
On Thursday, Huckabee told reporters that illegal immigration "comes up more than the Iraq war … It's absolutely on fire everywhere" as an issue.
Daniel Kowalski, editor of a technical journal for lawyers called Bender's Immigration Bulletin, said the illegal immigration disputes among the GOP candidates may resonate with those voters passionate about security borders.
The candidates are "trying to puff themselves up as the toughest," he said.
Contributing: Susan Page