The mix-up happened on Thursday night when the workers were called to inspect flooding near Exhibition Centre station beside the Scottish Event Campus, where the climate change conference opens on Sunday.
They were prevented for a time from reaching the rail line at an undisclosed access point believed to be in the vicinity of the high-security “Blue Zone” of the conference.
An industry source said: “A team of engineers sent to inspect a build up of water were not able to get in immediately because COP26 security stopped them.
"It was a miscommunication – they had permission, which has been agreed at high levels, but the security team on the ground were not aware of it.”
The engineers arrived with equipment in a van that they could not have moved onto the tracks via the station, which remains open.
The flooding did not disrupt trains at the station, which is expected to be used by thousands of people heading for the two-week summit.
ScotRail will run longer than normal trains to a maximum of six carriages on the Dalmuir to Motherwell/Larkhall line through the station to cope with demand, along with extra trains during the evening.
Security has been progressively increased around the Blue Zone as the conference approaches, with the Clydeside Expressway parallel to the line closed since last Saturday.
Roads around the station have also been closed to traffic except cycles since the weekend.
Finnieston Street, which runs close to the station, was also closed to traffic from Thursday.
A Network Rail spokesperson said: “Extra security is in place around the COP26 venue, including Exhibition Centre station.
"We have clear processes in place to facilitate access for our key workers during the conference and they have been working well over the past week.
"Due to miscommunication, a team of engineers inspecting a flood site were challenged by security, but the matter has been resolved.”
The UK Government, which is in charge of staging the conference, have been approached for comment.