The number of motorists caught tampering with their parking coupons has more than doubled following a crackdown.
About 1,960 were nabbed last year - up from an average of 950 a year between 2007 and 2011.
The most common method is to reuse old coupons by folding the tabs instead of tearing them off.
On Wednesday, the authorities said the offence is "tantamount to cheating". They now plan to extend the use of electronic parking systems, which avoid the problem by charging motorists automatically.
Most tampering happens in carparks run by the Urban Redevelopment Authority (URA).
This may be because URA carparks cater more to short-term parking where coupons are generally used - as opposed to the season-parking labels commonly used by residents leaving their vehicles in Housing Board carparks.
Last year, 1,560 motorists were caught by the URA, up from an average of 800 a year between 2007 and 2011.
Meanwhile, 400 were nabbed by the Housing Board, compared to an average of 150 in each of the preceding years.
Both agencies said the increase came after they stepped up enforcement at carparks, but gave no further details.
They added that they are increasing the use of electronic parking, which solves the problem of people tampering with their coupons.
The system, which employs CashCard technology and an in-vehicle unit reader, charges by the minute.
The HDB uses it in 344 out of its 1,800 carparks, up from 218 in January last year.
Meanwhile, the URA has installed it in 15 of its 122 off-street carparks.
Last September, only four of them had the system in place.
Motorists who spoke to The Straits Times said they usually steered clear of tampering with parking coupons. They were more likely to get fined for leaving their cars at carparks for too long.
Businessman P.S. Lim, 58, said that he had not tried to alter his coupon - and would find it "embarrassing" to be caught doing so.
"I don't think it's right," he added. "It's cheating. If you can afford to pay for a car and maintain it, you shouldn't be scrimping on a few dollars of parking fees."