The banner, bold and provocative, was tattooed with a syringe, skull and crossbones, and a call to action: “Say no to forced vaccination.’’

The message, delivered last week on Beacon Hill, was aimed at a seemingly prosaic piece of legislation that aims to better define - and, in some respects, restrict - the emergency powers of the state’s public health officials.

Within the bill’s arcane language, a 16-month-old activist coalition sees government authority run amok: mandated vaccinations, quarantines, arrests, fines. Swine flu, they warn, will be the virus that opens the door to the public health police.

“We have a concern that we will be forced to be quarantined if we refuse the vaccine,’’ said Laura Jackson, president of the Liberty Preservation Association of Massachusetts, which mustered 30 to 40 members for the lobbying drive. “What I’d like to see done with this law is have it burned.’’

Those concerns, public health authorities insist, are entirely unfounded. But the association’s multimedia campaign - aired over talk radio and its website - compelled state Public Health Commissioner John Auerbach to send an italicized, bold-faced missive to legislators, stressing that “mandatory vaccination is not and has never been part of the plan or discussion in Massachusetts’ pandemic response.’’

The bill, Auerbach and other top officials said in interviews, would never force anyone to be vaccinated unwillingly, and its extraordinary measures - such as quarantining people who decline inoculations - would be reserved for equally extraordinary times, such as a bioterror attack or the emergence of a highly lethal, rapidly spreading germ. Swine flu, caused by the H1N1 virus, is not such a germ, Auerbach said.

The protest by the group, whose founders supported Republican Ron Paul in the 2008 presidential election, reached its pitch at an especially delicate moment for public health authorities. Auerbach’s letter demonstrates that his agency is worried the dissent could raise doubts about vaccination and imperil an unprecedented campaign to inoculate millions this fall against the seasonal flu and the swine strain.

“Accuracy of information is going to be key in terms of the public understanding what they should do,’’ Auerbach said in an interview.

In the opposition to Massachusetts’ revised public health emergency law, as well as in the combustible health care town hall meetings that greeted some members of Congress this summer, analysts see more than traditional conservative concerns about individual liberty and big government.

They also find signs of deeper worries about a world descending into uncertainty, with panic over economics and the emergence of a novel flu strain.