Dr Helmut Marko says Mercedes could have gained a one second per lap advantage by testing between the Spanish and Monaco grands prix.
A controversy has erupted over Mercedes' 'secret' three-day, 1000km tyre test in Barcelona, before Nico Rosberg strolled from pole to victory in Monaco.
Red Bull's Marko told German broadcaster Sky that Pirelli did not ask the world champion team if it wanted to conduct the running.
"We are very unhappy," said the Austrian. "When we test for three days, we go a second faster -- that's what Adrian Newey says.
"It definitely helped them -- you can see that they had no tyre problems today. That's no accident," added Marko.
Red Bull and Ferrari have lodged an official protest, which is being heard by the FIA in the immediate aftermath of the Monaco grand prix.
"There are sporting regulations," said Marko, "that cannot be overriden by a civil agreement between Pirelli and the FIA.
"The sporting regulations state clearly when and how you can test."
He said Red Bull is seeking "a clarification of how to proceed in the future, and that the competitive advantage of Mercedes is compensated in some way".
