The organisation posted a tweet comparing its ad from September 2015 with a new ad from Specsavers released this month.
Smart Energy GB's ad shows a man painting line markings on a football pitch. The camera zooms out to show his higgledy-piggledy attempts, with the slogan: "Why estimate when you can be accurate?"
The newer "Football pitch" ad from Specsavers, launched last week, similarly shows a man incorrectly marking out the lines on a football pitch. It concludes with the Specsavers tagline: "Should've gone to Specsavers."
Gavin Sheppard, director of marketing at Smart Energy GB, said: "I wouldn’t go as far as to quote Oscar Wilde in saying 'Imitation is the sincerest form of flattery that mediocrity can pay to greatness', but you don’t need to have gone to Specsavers to see where their inspiration came from for this ad.
"When household name brands start taking your ideas, you know you’re doing it right!"
But Specsavers denied any intentional copying, with a spokesman telling Campaign: "Any similarity between the two advertisements is purely coincidental."