Drivers who parked their cars on national land in the parliamentary triangle on April 27 without buying a ticket because they believed it was a public holiday have been told to pay the $97 fine or take the matter to court.

People who argued they should not have to pay the fine started receiving letters this week informing them the NCA was solid in its conviction.

The NCA told The Canberra Times 110 fines were issued on April 27 in the parliamentary triangle.

If all of those infringements were issued for parking without a valid ticket, it means more than $10,000 in fines were dished out under circumstances some found confusing.

The day was not officially a public holiday, but was given as a day off in lieu for ACT public servants and some federal government departments.

ACTION bus drivers operated on a weekend schedule and the territory's public schools were closed.

The rest of the working population went to their jobs.

Those enjoying an official day off work saw signs in car parks telling them they did not need to pay for parking on public holidays.

"A small minority have applied to have the infringements withdrawn," an NCA spokeswoman said.

"April 27 was not gazetted as a public holiday in the ACT ... It was a normal day of work.

"The ACT government, certain federal departments and workers with conditions within their certified agreements were granted a day in lieu for Saturday April 25."

She said there was a legislative requirement to pay for parking if the signage in the area stated that payment was required.

"NCA parking areas are all clearly sign posted as pay parking, between 8.30am and 5.00pm, Monday to Friday, public holidays excepted," the spokeswoman said.

"As such there is no ability for the NCA to withdraw a fine because people thought it was a holiday, the fines were issued correctly."