“But I can't say it will be this color or that community. That's too complicated," she added.
Discrimination on the basis of color, gender, nationality, sexual orientation or religious belief is illegal in France.
SOS Racisme said the 69 offices it called were all affiliates of France's leading temp firms, with billions of euros (dollars) in combined revenues.
It said 55% of the branch offices it contacted refused requests to discriminate.
But 39% of those called agreed to weed people out on racial grounds, the campaign group said.
The remaining 6% also refused to racially select candidates but suggested that the fictitious firm do so itself, SOS Racisme said.
Although limited in scope to a small number of agencies, the findings highlight what anti-racism campaigners say is a wider problem of discrimination in some French workplaces.
Previous research has shown discrimination against job-seekers from neighborhoods with immigrant populations or with names that aren't traditionally French.
The government’s minister for equal rights, Elisabeth Moreno, noted that such actions are illegal and said the companies would be summoned for a meeting.
“Discrimination is a daily plague that we can all be victim or witness to, and that we must absolutely wipe out,” Moreno said in a statement.