ComfortDelGro Corp's largest shareholder, the Singapore Labour Foundation, has pared down its stake in the transport giant again.

The Straits Times understands the labour body has sold 170 million of its ComfortDelGro shares for about $332 million. This is out of the 252.6 million - or close to 12 per cent share - it previously owned.

The amount raised indicates that SLF had unloaded the shares below ComfortDelGro's last transacted price of $2.18.

This sale makes the Capital Group Companies the largest stakeholder in ComfortDelGro. Capital Group has 6.41 per cent now.

SLF has been paring down its stake in the transport group since its formation 10 years ago. It started with close to 19 per cent of the group, but in 2006, sold 6 per cent off.

It is not known why SLF is diluting its share. The foundation was not reachable for comment, but a director told The Straits Times it was a regular "rebalancing" of its portfolio the foundation undertook regularly.

That was the same reason it gave back in 2006. Back then, the SLF gave an undertaking that it would not sell off anymore shares for two years. "That agreed period has passed," said the director.

The sell-off has spooked the market. ComfortDelGro's share price fell to as low as $1.89 Thursday morning.