The phrase "a picket of" is correct and usable in written English.
It can be used when referring to a group of people who are protesting or demonstrating, typically in a labor context.
Example: "The workers organized a picket of their workplace to demand better wages and working conditions."
Alternatives: "a protest of" or "a demonstration of".
Protesters lined the edge of the road facing a picket of riot police.
A picket of Shia clerics tried, without much success, to keep them from breaking ranks and treading on the crops.
Outside the regional parliament in Barcelona recently stood a picket of noisy secessionists, including a bare-breasted woman with a separatist flag around her neck.
The general pointed to a fence in the distance, a picket of watch towers, a dusty road driven by an Israeli armored personnel carrier — and beyond it, Jordan.
A picket of about 200 pro-Palestinian demonstrators campaigning under the title "Block the Boat" assembled on Saturday alongside the Zim Shanghai, a massive, 300-meter commercial vessel.
I understand that anger, even if I wish it was being channelled into a picket of George Osborne's office rather than at other artists.
"I'm thinking of organizing a picket line of pregnant women and women with small children, and I'll put them in front of this judge's apartment.
Shortly after the strike began, all 35 S.A.G. film actors on the New York set of "Perfume" crossed a picket line of stage employees protesting a nonunion crew.
While young, Fertig saw a picket line of white parents protesting the admission of a black student whose parents had moved to the community.
He said the stretch of the border a few miles north of Malone was being guarded by a "picket line" of officers.
A picket line of about two hundred D.C. workers snaked in front of the hotel entrance, discouraging any would-be guests from getting a room for the night.
