More than 50 protesters gathered outside Mauna Kea in Hilo, Hawai'i to oppose the construction of a thirty-metre telescope.
Astronomers say Mauna Kea is the ideal location for observation and to understand mysteries of the universe.
The telescope is expected to create 300 full-time construction jobs and 120 to 140 permanent jobs.
The activists, most of whom are Native Hawaiians, walked from one part of the Mauna Kea Access Road to the other blocking 15 vehicles which were transporting workers up to the site. They did, however, allow visitors and other telescope operators through.
Some say the $1.4 billion project is a "desecration of the mountain", the mountain which is regarded by many as sacred.
While protesters strongly disagree with this project, the message they are portraying is about aloha and not anger towards the workers.
In the video below, protesters are seen lining the road bearing flags, singing traditional Hawaiian songs.
Video credit: Big Island Video News - TMT Opposition on Mauna Kea
Protesters have had a heavy presence outside the visitor centre since last week following the arrival of construction equipment.