The Terriers were left incensed by the change of heart from the officials after Mason had initially pointed to the spot following a tussle between Bluebirds defender Joe Bennett and Florent Hadergjonaj.
With Philip Billing having already picked up the ball in readiness for the penalty, Mason, after speaking to assistant Stuart Burt, suddenly reversed his decision and awarded a free-kick to the home side.
“I really cannot find the words how this can happen,” said Wagner, whose side remain eight points adrift of safety.
“The fourth official (Andre Marriner) had no idea either. He was as surprised as everyone else was.
“Decisions like this make tables and seasons.
“We have had so many decisions against us and I don’t know why.
“It was clearly a penalty, the video footage speaks for itself and we have not got it.
“I know they (the officials) have a very difficult job.
“But sometimes they make it much more difficult for themselves.
“The referee even gave them the ball. I have no clue what was in their head.
“After seeing the footage it is a clear penalty.
“But I don’t know how many decisions like this have gone against us this season.
“We will probably get another phone call from the FA, apologising for the decision.
“Six weeks ago our negative run started with one of the worst displays for Michael Oliver against Brighton when he made a mistake (in dismissing Steve Mounie).”
Unsurprisingly Cardiff manager Neil Warnock had a different take on the 76th-minute incident that was Saturday’s main talking point.
“I think it is good there was an experienced linesman,” said the Bluebirds’ chief.
“There was not enough contact for a penalty and the linesman made him change his mind.
“If that had won them the game I would have been disappointed. I also think there was a clear penalty for us on Junior Hoilett in the first half – the lad (Hadergjonaj) did not see him coming and took him out.”
The draw in south Wales ended Town’s eight-game losing run, but did little to improve their survival prospects on an afternoon when rivals Burnley and Southampton both won.
“I said before this game that we had to win it and we have not done that,” added Wagner, whose side face champions Manchester City in their next league outing.
“Clearly we were the more active team and we deserved something. The spirit and attitude was there.
“But it shows how big decisions are important in this game.
“It is something you cannot control.”
Huddersfield remain bottom of the table and eight points adrift of Cardiff, who failed to manage a single attempt on target in what was a poor display from the home side.
But Warnock – the former Huddersfield Town manager – said neither of his two frontmen, Callum Paterson and Victor Camarasa, were fully fit, adding: “They have helped me out.
“Camarasa has got a muscle injury from last week and Paterson couldn’t get around like he normally does.
“It would have been easy to have lost that game in the last few minutes. But that’s our sixth clean sheet, which is good. If you cannot win then you get a point.”
Report: Page 2