Union members clashed with mounted police at a building site in Melbourne on Tuesday morning.
Members of the Construction, Forestry, Mining & Energy Union have been blockading a Grocon Construction building site since last Wednesday.
The company was granted a Supreme Court injunction last week, banning union organisers from the site.
Around 130 contractors have been unable to get into the site because of the blockade.
The ABC reports union members succeeded in pushing police horses back. There are also reports that construction workers from the city are leaving their worksites and heading to the area.
State Police said they were helping Grocon employees to "safely enter their workplace."
In a statement, police said it is a civil matter between the union and the company. Streets in the area are blocked until further notice.