SAN FRANCISCO — When David North, the editorial chairman of the World Socialist Web Site, noticed a drop in the site’s traffic in April, he initially chalked it up to news fatigue over President Trump or a shift in political consciousness.

But when he dug into the numbers, Mr. North said, he found a clearer explanation: Google had stopped redirecting search queries to the site. He discovered that the top search terms that once brought people to the World Socialist Web Site were now coming up empty.

“This is not an accident,” Mr. North said. “This is some form of deliberate intervention.”

Accusations that Google has tampered with search results are not uncommon and date back to the earliest days of its search engine. But they are taking on new life amid concerns that technology behemoths are directly — or indirectly — censoring controversial subjects in their response to concerns over so-called fake news and the 2016 presidential election.

In April, Google announced an initiative called Project Owl to provide “algorithmic updates to surface more authoritative content” and stamp out fake news stories from its search results.