"The Democratic Alliance is receiving reports that helicopters belonging to the SA Police Service [SAPS] Air Wing have been grounded for months," DA MP Dianne Kohler Barnard said in a statement.
She said 15 of the air wing's 37 helicopters were on the ground awaiting "routine" inspection, while three more were in a hangar in Cape Town awaiting repairs.
"This now brings the total of grounded SAPS helicopters, which we know of, to 18 out of 37. This is nearly half of the entire air wing," said Kohler Barnard.
Contacted for comment, police ministry spokesperson Zweli Mnisi accused Kohler Barnard of politicising police operational matters.
"Since when is Kohler-Barnard a technical expert on air wings? Does she even know when and under [what] conditions the helicopters must be airborne, or go for maintenance? We do not think so."
Mnisi said the ministry had emphasised the principle of cost effectiveness across the department to SAPS management. This included the maintenance and control of aircraft.
"These [helicopters] are instruments of [our] trade, which enable police to fight crime; as such, they cannot be [in the] air for the fun of it.
"We therefore support our management when they properly manage the fleet and, further, encourage them to do so; they must ignore prophets of doom, who are attempting to politicise even operational matters."
He suggested the DA was trying to use the SAPS for political purposes.
"They have failed before, and they will still fail in their endeavours to utilise SAPS as a political tool to project their own interests."
In her statement, Kohler Barnard said "various sources" claimed maintenance of the helicopters had not been carried out "because SAPS has yet to decide who should be awarded the service contract".
The grounded helicopters had cost between R15m and R20m each. "This means that nearly R300m worth of crime-fighting equipment is not currently being used to keep our citizens safe."
In addition, the Robinson R44 helicopters, which the SAPS bought ahead of the 2010 World Cup, "are apparently yet to be used".
The Robinson helicopters - the SAPS was thought to have bought four - were fitted with specialised crime-fighting equipment, such as searchlights and infra-red technology.
Kohler Barnard said she would be submitting parliamentary questions to try and establish what was happening with the air wing's helicopters.
"These helicopters should not be sitting around in the hangars, waiting for the SAPS to decide who should be given a contract to maintain them. They need to be in the sky, tracking down the criminals who terrorise our communities," she said.
Officials at the police department's communications unit were not immediately available for comment.