A group holding banners were seen walking and chanting “No new gas. No new coal. Insulate Britain” as they made their way from Moorgate to London Wall.
A number of City of London Police officers were following the group.
“We’re aware of a slow-walking protest group making their way from Moorgate towards the Museum of London, travelling on the carriageway,” City of London Police said.
“Traffic will be affected. Officers are on the scene.”
Protesters stopped traffic in Shepherds Bush Green, west London, and Aldwych in a similar demonstration on Monday morning.
It comes as the group, which opposes all new oil and gas licences in the UK, has changed its approach to protesting. Instead of blocking traffic entirely by gluing themselves to the road - which has led to a number of arrests - they are slowing traffic down by walking.
The disruption follows reports over the weekend of a government-directed police “crackdown” on action by groups such as Just Stop Oil.