Cab operators in Singapore are upping taxi flagdown fares on the sly.

ComfortDelgro, which owns 60 percent of Singapore's 27,400 taxis, has priced its new Hyundai i40's initial fare at $3.70.

This is 50 cents higher than the flagdown for the older Sonata, which currently makes up more than 85 percent of the taxi giant's fleet.

However, the Sonatas are expected to be replaced by the i40 over the next few years.

Cab operators have justified the increase as a move to counter higher certificate of entitlement prices. COE premiums for taxis are now $77,000, up from $50,000 two years ago.

And another reason for the higher price is to pay for the introduction of newer "green" hybrid cabs.

SMRT, the third-largest operator, has ordered more than 600 Toyota Priuses.

The first units will hit the road on Friday, with a flagdown of $3.80.

Cab operators Premier and Prime are charging $3.50 to $3.70 for their Prius cabs.

Taxi fares are not regulated in Singapore. The common practice is for cab operators across the board to increase fares in tandem.

Trans-Cab, the second largest taxi firm with about 4,400 cabs, has priced its Renault Latitudes, introduced two months ago, at $3.90.

This is up from its similar-sized Chevrolet Epica, which costs $3.60 to flag down now, and $3.40 just a few weeks ago.

SMRT will also raise the rate for its Hyundai Azera to $3.80 this week, from $3.60.

Top photo from here