Shell has been fined £40,000 for errors in reporting on emissions from Mossmorran.
The company said the administrative slip-up had no impact on actual levels of carbon dioxide given off by the controversial plant.
However, Mid Scotland and Fife Green MSP Mark Ruskell claimed the latest breach of regulations at Mossmorran raised fresh concerns about its future.
Environmental watchdog, the Scottish Environment Protection Agency, said Shell had been fined for failing to comply with its greenhouse gas emissions permit, as it did not submit sufficient allowances to cover its annual reportable emissions from 2013 to 2015.
Mr Ruskell said: “This is a significant breach of regulations by Shell and yet another example of the company stumbling over environmental and safety compliance.
“Reducing our greenhouse gas emissions is a collective responsibility for all of society, and it’s not enough to just say sorry and move on.”
He claimed a lack of investment and an aging plant meant errors were more likely to occur.
“The issues that need to be addressed in SEPA and the HSE’s current investigation are now stacking up, and it seriously needs to consider whether this plant can continue to operate as it is,” he added.
A spokesperson for Shell UK Limited said the company had identified an issue with a historical emissions reporting calculation at the Fife NGL plant.
The firm corrected the calculation and immediately disclosed updated data to SEPA to rectify the error.
“We very much regret this situation,” he added.
“Shell prioritises the safety of our staff, community and care for the environment.
“The inadvertent reporting error had no impact on actual levels of carbon dioxide emitted by the plant.”
It was a metering error which resulted in the inaccuracy.
Shell; said the cause was in the metering and data transfer of volumes of fuel used by a single propane unit at the plant.
As a result propane unit volumes had been under reported by around 0.5%
Shell wrote a letter to the local community on July 12 explaining what had occurred and apologising for the error.