Mercedes have won the Drivers’ and Constructors’ Championships for the past five years and are well on track to continue their dominance this campaign.
Lewis Hamilton has dominated the opening seven races of the season, winning five.
But Marko reckons the Silver Arrows had an advantage when building their 2019 car and were afforded some early tip-offs.
“Let’s put it this way,” Marko told Auto Bild.
“It’s noticeable that the rule changes and decisions lately have always been good for Mercedes.
“For example, Pirelli changed the tyres for 2019 so they do not overheat, but last year only Mercedes had a problem with them.
“Suddenly in 2019 only Mercedes always gets the temperatures in the correct working window. Everyone else not.
“The concepts of all the cars was for less downforce. Only Mercedes built a car with a lot of downforce and traction, and in hindsight that was exactly the way to get the most from these new tyres.
“I cannot prove that Mercedes got data earlier than us, but I cannot rule it out.
“We at Red Bull will look very closely at the future development of Formula 1 and there will also be discussions with Pirelli.”
Mercedes boss Toto Wolff played down the accusations.
“We cannot be distracted by such voices,” he replied.
“Every year we get new tyres from Pirelli. Sometimes you understand them faster, sometimes you have more trouble with them, and as fair competitors, we make the most of what’s given to us.”
Hamilton controversially won the Canadian Grand Prix last weekend after Sebastian Vettel was slapped with a five-second penalty.
It means the Brit is 29 points ahead of team-mate Valtteri Bottas and 62 ahead of Vettel.