The pair tussled at Stowe, with Stroll passing Gasly for 11th off the track before they came together at Club later in the race.
The contact left Gasly with terminal suspension damage, while Stroll received a five-second penalty for causing the collision.
Asked by Autosport what had happened during the pair's battle, Gasly said: "To me it was quite clear and it's been always in the regulation he can't leave the track and gaining an advantage.
"On everything that I've seen he had four wheels off the track passing me, and that's gaining an advantage.
"I got down 15 seconds last weekend for track limits, now I lose a position today [because] someone getting off the track and nothing happens.
"Formula 2, Victor Martins was in the lead and got a five-second penalty for the exact same thing, so I'm just extremely confused with what's going on at the moment.
"And it just changes what follows after that... Get back behind him, I managed to get past him on the outside of Turn 7, after I managed to get past Carlos there, [he] passed us back.
"And then Lance takes us out of the race in the last chicane. So just extremely disappointed because the first part of the race was going well.
"We were chasing Fernando, there was good speed. I just lacked some straightline speed to try something and get a move on him, but it was still good to be in that pack, and then all our efforts get ruined with what followed. So disappointed."
He added: "Well if you go off the track, you got to give the position back. Just as simple as that.
"If you try and you see you've been off the track, just give the position back, and that's how I've been told racing by FIA. I've paid the price in different situations.
"It's just not fair not having that consistency. Now next race, I'm supposing that going off the line, off the track overtaking someone is allowed.
"Then all of a sudden, you're going to end up with a five-second penalty. So I just can't understand. And it's... It just doesn't seem fair.
"It's black and white. Track limits, black and white, you either on the track or off the track. Off the race track gaining an advantage - that's the five-second penalty or give the position back.
"Always happening. And it happened with Victor this morning. So it's just... I don't understand that."
Though Gasly accepted that he "potentially" could have left Stroll more space on the outside, he said he had given him space to leave one wheel on the racing line but he "didn't do it."
He said he would be speaking to the FIA for clarification after the incident because it's "got to be crystal clear" and also said he would discuss the incident with Stroll.
"We're racing at 350 km/h, at the moment which... different situations," he said. "Last week, we got penalised for stuff where we feel like we're not getting the warning properly.
"This situation for me as soon as I saw him going off the track, I was like he'll give the position back. And I spent three laps behind losing time in his gearbox where I should not be there.
"So just asking for consistency. If that's allowed, fine. But it's got to be allowed for everyone."
Additional reporting by Adam Cooper
