HRT on Saturday joined Virgin in refusing to rule out lodging a mass protest after Sunday's Spanish grand prix.
FIA technical delegate Charlie Whiting on Friday said most of the field is technically afoul the regulations at present due to their sophisticated blown exhaust systems.
HRT, Virgin and - perhaps - Williams are not running those systems this weekend, and Virgin's Graeme Lowdon played down the prospect of a protest as "highly unlikely".
HRT team boss Colin Kolles, however, sounded more likely to push the button.
"I think some teams are running illegally, simple as that," he told Reuters.
Asked if he will protest, he replied: "Maybe, I don't know. I will see."
Some may accuse Hispania of taking advantage of its inferior technical situation, but Kolles insists the team was readying a blown diffuser for debut this weekend.
Then came the FIA clarification.
I think some teams are running illegally, simple as that
"He (technical boss Geoff Willis) said 'No, we have to review this because there is this clarification from the FIA'," continued Kolles.
"So we basically went then in a different direction and two days later you (the FIA) change it, and I am not happy with this."