Harbhajan, who picked up two wickets in each innings as India won the second Test by 195 runs against Pakistan in Calcutta, was reported for chucking when bowling his 'doosra', the delivery which spins away from right-handers.
"The report relates specifically to the bowler's action when delivering the `doosra'," said match referee Chris Broad.
"It was noticeable to the umpires and me that there was an apparent change in action when bowling this delivery between the first innings of the match, when no concerns were raised, and the second, which then prompted the report to be made."
The ICC said Singh will now undergo independent analysis of his action by a member of its panel of human movement specialists.
Harbhajan, 24, was cleared earlier this month after being reported for bowling his 'doosra' during the second Test against Bangladesh in Chittagong in December. The spinner underwent work with Australian bio-mechanics expert Bruce Elliot.
The ICC introduced a new threshold on March 1 allowing all bowlers to straighten their arms by up to 15 degrees.
Previously, spinners were only permitted to straighten their arms by five degrees, medium pacers 7.5 and fast bowlers by 10.
Harbhajan was also reported for a suspect action in 1998, but was cleared.
