Opponents say the $16-million project runs through arable fields and untouched woods, as well as a popular hiking trail and a fishing area.
A small group stopped wood harvesters from working on Thursday, and returned to the site today.
The provincial Transportation Department started putting up fencing on Thursday around the construction site about 30 kilometres west of Charlottetown.
However, protesters entered a clear-cut area early today before the fencing was complete.
A small group made their way down to the construction site and stopped a harvester as soon as work started around 7 a.m..
The same protesters spent part of the morning piling fallen trees into makeshift teepees and then leaned trees against the tree harvester, almost hiding it from view on one side.