The measure would put people caught surreptitiously recording agricultural operations in jail for up to a year and fine them $5,000.
The bill, which now goes to the House, stems from a 2012 incident at Idaho's Bettencourt Dairy in Hansen where activists from the group Mercy for Animals captured images of workers caning, beating and stomping on cows.
Idaho's $2.5 billion milk industry argues the video was used by "agri-terrorists" not merely to curb abuse, but to harm the dairy's business even after its owner fired workers and pursued animal-cruelty prosecution.
Representative Sen. Jim Patrick, the sponsor from Idaho's dairy heartland surrounding Twin Falls, argued that no less than the state's food safety is at stake, invoking the specter of groups including al-Qaida sneaking onto Idaho farms and putting crops and other commodities at risk.
"We as a nation are at risk of losing a lot of our food to terrorism," Patrick said.
Other proponents put it in plainer terms: Dairy owners should be able to expect people working for them aren't lying on their job applications simply to sneak onto their facilities.
In addition to the filming provisions, the bill would criminalize obtaining records from such operations by force or misrepresentation, while lying on an employment application for such a farm would also be outlawed.
Legitimate whistleblowers who see abuse can still report it to the Idaho Department of Agriculture, whether this bill passes or not, said Sen. Todd Lakey, R-Nampa.
"To me, this does not limit the ability of an individual to file a complaint," Lakey said. "It does not limit constitutionally protected speech. To me, it comes down to private-property rights."
Foes of the measure came from the ranks of the Senate's civil liberties defenders who worried the bill is so broadly written that it could be interpreted to outlaw even legitimate activities.
Republican Sen. Curt McKenzie branded the measure too extreme, especially when there are already trespassing provisions in Idaho's code to punish people who go onto somebody's property without permission.
"It may go beyond what we intend," McKenzie, R-Nampa, said.
Meanwhile, Democrats compared animal-rights activists to the groundbreaking muckraking journalist Upton Sinclair, whose 1906 book "The Jungle" about the Chicago meatpacking industry helped spur changes that improved food safety and working conditions.
Senate Minority Leader Michelle Stennett, D-Ketchum, said the bill might actually backfire, undermining public confidence in the sincerity of Idaho dairies to protect their production animals.
"This bill creates a perception the industry is hiding animal abuse," Stennett said.
Utah has a similar "ag-gag law," though it's currently the target of a challenge in U.S. District Court on, among other things, free-speech grounds.