UNIONS have condemned a ''violent and threatening attack'' on workers after police dismantled a blockade at a Visy factory in Dandenong and arrested 29 men.

Australian Manufacturing Workers Union national secretary Dave Oliver attacked the ''totally out of hand'' police response to a peaceful protest, which came after Visy won a Supreme Court injunction last Friday to allow access to and from the site.

Police arrest a picketing worker outside the Visy carboard plant in Dandenong yesterday. The action allowed trucks to enter the site for the first time in more than a week. Credit:Rob Carew

Protesters were forcibly removed by police yesterday morning and taken away in divisional vans. The arrests for undue obstruction and besetting premises allowed trucks to enter the site after a blockade and strike of more than a week had stopped access.

Mr Oliver wrote to Police Minister Peter Ryan saying he had serious concerns about the police's role and said it had ''significantly escalated'' tension at the protest. He said one worker had a suspected heart attack at the scene.