McLaren's Lewis Hamilton has urged stewards in Monaco to keep an eye on Toro Rosso's drivers, accusing them of holding him up in Spain last week and helping title rival Sebastian Vettel.
World champion Vettel's Red Bull and Italian-based Toro Rosso are sister teams, although independently run.
Hamilton finished second to Vettel in Barcelona but feels Sebastien Buemi and Jaime Alguersuari hindered overtaking.
"They [Toro Rosso] let Vettel past and then they held me up," said Hamilton.
The Red Bull and McLaren drivers lapped all the teams in that race in Barcelona but they will have a far harder time on Sunday getting past on the narrow Monaco streets, where overtaking is notoriously difficult.
"Definitely in the last race there was some of that [being held up], all of a sudden they [Buemi and Alguersuari] were moving in my way, causing a bigger gap," said Hamilton.
"The gap that I closed to him [Vettel] I lost. That wasn't cool.
"If that continues to happen then some penalties should probably be handed out," added the 2008 world champion, who won in Monaco that same year
"I just hope that the stewards are wary of it, and I'm sure they'll do a great job of it."
Hamilton is the only driver to beat Vettel so far this season, winning in China thanks to clever strategy despite having a slower car.
The Briton is 41 points adrift after five races but has high hopes for Monaco, his favourite street circuit.
Vettel has yet to win in Monaco, but set the fastest time in Thursday's first practice. Hamilton was second fastest in an afternoon session led by Ferrari's Fernando Alonso.
Red Bull team boss Christian Horner scoffed at Hamilton's concerns.
"Believe me, Toro Rosso drivers have often had that complaint from our own drivers as well," said Horner.
"You've only got to look at Abu Dhabi last year to see that with Mark Webber. Absolutely not, there's no discussion between the teams.
"The teams operate totally independently, there's no tactics to help one or the other."
Webber finished eighth in Abu Dhabi in last season's final race, his title hopes disappearing after he became stuck in traffic at a circuit where overtaking is as hard as Monaco. Alguersuari was ninth.
Hamilton's team mate Jenson Button also doubted there had been any collusion between the Red Bull teams.
"They never have before, and it's not the same team," he said. "I think Buemi and Alguersuari would love to beat Sebastian and Mark. I've never had an issue before and I don't expect to see one in the future."