Red Bull made a formal protest at the Monaco Grand Prix on Sunday after learning that Mercedes carried out a secret tyre test with Pirelli in Spain last week.
Red Bull team principal Christian Horner, who found out 'second hand' only on Saturday night, suggested Mercedes had gained an unfair advantage and said his team had sought a clarification of the rules.
"We feel it's not in line with the rules, so that's why we've protested before the race here. We just want clarity," he told Sky Sports television.
"I think it's important (that it) be brought to a head. I don't think we're the only team that feels that way."
Formula One regulations ban in-season testing but Pirelli said their contract stipulated that they could do 1000km private tests with a 'representative' car and the three days in Spain were legal.
Mercedes GP non-executive chairman Niki Lauda said the team had obtained permission from the International Automobile Federation.
''The FIA confirmed it and said 'yes' and so therefore we did the test. We think other teams have been asked too," he said.
Pirelli motorsport head Paul Hembery said the test in Barcelona after the Spanish Grand Prix was not the first of its kind.
"We've done it before with another team and we've asked another team to do some work as well," he said.