The incident happened in the 50th and final over of England's innings in their World Cup clash when Lakmal bowled a second consecutive high, full pitched ball to Buttler, after being given a first and final warning by on-field umpire Rod Tucker earlier during the same over, reports AFP.
Lakmal was stopped from bowling at Wellington's Westpace Stadium and reported to the match referee David Boon for dangerous and unfair bowling.
He was also fined 30 percent of his match fee after pleading guilty to breaching rules that relate to "conduct contrary to the spirit of the game".
"While making my decision, I took into account that it is was dangerous and unfair bowling, there were no mitigating circumstances, and there was no remorse from the bowler," said former Australia batsman Boon.
Sri Lanka won the match by nine wickets, although Lakmal ended with expensive figures of one for 71 from 7.4 overs.
Image: Suranga Lakmal
Photograph: Anthony Phelps/Reuters
Sri Lanka's Herath doubtful for Australia clash
Scotland fined for slow over-rate vs Afghanistan
World Cup blog: Minnows are crucial to cricket
Kiwis head into World Cup with thumping win over Pakistan
PHOTOS: Sri Lanka thump Bangladesh for second straight win