The claim from Glasgow Labour MSP Paul Sweeney came as he raised an urgent Parliamentary question at Holyrood to ask what the Scottish Government was doing to resolve the pay dispute after strikes were called during the two-week event in Glasgow next month.
The Unite union announced on Monday it would step up its work-to-rule since September 24 with strikes before and during the Cop26 conference - for which extra ScotRail services are due to run to cope with extra demand.
Unite members maintain the Abellio-run operator's trains, with the strikes on October 18-19, November 1-2, November 10-11, and November 12-13 potentially reducing the number which are available to run.
However, ScotRail said Unite's action to date had not reduced the number of carriages in service.
The Rail, Maritime and Transport union has also called a strike ballot for stoppages during the conference.
Mr Sweeney said: "We now face the prospect of Scotland being an international laughing stock as delegates of the Cop26 conference can’t use public transport because of Abellio’s intransigence and this government’s seeming indifference.
"The situation should never have been allowed to deteriorate to this point.”
However, transport minister Graeme Day said: “Talks with the trade unions over the general grades’ pay claim took place today and discussions are planned tomorrow with [drivers’ union] Aslef.
He said the main talks were due to resume on Thursday.
The minister had earlier told BBC Radio Scotland a revised offer was expected to made after ScotRail offered a 2.2 per cent rise in return for savings that could include ticket office closures - as The Scotsman revealed last Thursday.
Mr Dey said: “Despite a backdrop of significant financial challenges faced by the rail sector, there are reasonable offers on the table which, through pragmatic and meaningful discussions about efficiencies and modernisation, could lead to an agreement being reached.
"Any cancellations as a result of industrial action not only have the potential to undermine the recovery of our rail services but also impact on vital revenue streams from ticket streams.
"While we support the right of every worker and trade union to engage with their employers to seek a pay deal, Cop26 is Scotland and Glasgow's chance to showcase the key role we see for rail in our sustainable future on a world stage.
"We obviously hope that staff and the unions will understand the importance of the moment and will work with ScotRail to resolve this dispute."
Mr Sweeney, who is a Unite member, also claimed 20 ScotRail staff at depots across Scotland had been sent home – “effectively locked out of their workplaces” – for refusing to operate machinery for which they did not have the necessary accreditation or training.
Mr Dey said: “There were a number of staff members who may have found themselves in that situation, and we have raised this issue with ScotRail.
"But in an industrial dispute like this, there is a lot of rhetoric, there is a lot of assertion, there is a lot of claim.
"What we need here is for calm heads, for people to get round the table and work constructively to resolve everything within this situation.”