In one of the demonstrations, some 70 berry pickers locked six of their team leaders in a room at the former school where they were living.
“Six of them were locked in, they were Vietnamese foremen, and in addition to being locked in, they were beaten up and two of the six were tied up,” Hans-Åke Hedin of the Dalarna county police told AFP.
The six were freed and police are looking for those responsible, he added.
Around 50 Vietnamese workers marched from their living quarters and staged a sit down protest along a road in the northern town of Nordmaling, said Magnus Haglund of the local municipality.
“I don’t know what they want, they have had little contact with the municipality,” Haglund told AFP.
“Those who represent their living quarters and have agreements with the berry company and the staffing company in Vietnam have tried to convince them to return (to work) to solve the conflict,” he said.
Last Friday, around 120 Chinese seasonal berry pickers in northern Sweden went on a 15-kilometre (9.3-mile) nighttime march to protest their salaries.
Thousands of seasonal workers from Asia, most of them from Thailand, come to Sweden each summer mainly to pick wild berries in the north under sometimes difficult working conditions.
After a disastrous season last year sent many of the foreign berry pickers home weighed down by debt instead of profits, they have this year for the first time been provided with contracts guaranteeing them a monthly wage of at least 16,372 kronor ($2,321).
Some Swedish unions however say the minimum salary is insufficient, pointing out that it in some cases is hardly enough to cover the money the workers have to shell out for things like plane tickets, housing and car rental.