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Something is puzzling on Facebook.

Early last year, soon after Facebook instituted a feature that let people subscribe to others’ feeds without being friends, I quickly amassed a healthy “subscriber” list of about 25,000 people.

Every Sunday morning, I started sharing my weekly column with this newfound entourage. Those posts garnered a good response. For example, a column about my 2012 New Year’s resolution to take a break from electronics gathered 535 “likes” and 53 “reshares.” Another, about Mark Zuckerberg, Facebook’s founder and chief executive, owing me $50 after the company’s public offering, quickly drew 323 likes and 88 reshares.

Since then, my subscribers have grown to number 400,000. Yet now, when I share my column, something different happens. Guess how many people like and reshare the links I post?

If your answer was over two digits, you’re wrong.

From the four columns I shared in January, I have averaged 30 likes and two shares a post. Some attract as few as 11 likes. Photo interaction has plummeted, too. A year ago, pictures would receive thousands of likes each; now, they average 100. I checked the feeds of other tech bloggers, including MG Siegler of TechCrunch and reporters from The New York Times, and the same drop has occurred.

What changed? I recently tried a little experiment. I paid Facebook $7 to promote my column to my friends using the company’s sponsored advertising tool.

To my surprise, I saw a 1,000 percent increase in the interaction on a link I posted, which had 130 likes and 30 reshares in just a few hours. It seems as if Facebook is not only promoting my links on news feeds when I pay for them, but also possibly suppressing the ones I do not pay for.

Facebook proudly informed me in a message that 5.2 times as many people had seen my post because I had paid the company to show it to them. Gee whiz. Thanks, Facebook.

This may be great news for advertisers, but I felt slightly duped. I’ve stayed on Facebook after its repeated privacy violations partly because I foolishly believed there was some sort of democratic approach to sharing freely with others. The company persuaded us to share under that premise and is now turning it inside out by requiring us to pay for people to see what we post.

Facebook takes a different view, saying that it is still finding the right balance for the algorithm that decides what people see in their news feeds.

“The two aren’t related; we don’t have an incentive to reduce the distribution that you send to your followers so that we can show you more ads,” said Will Cathcart, product manager for Facebook’s news feed.

“The impact ads are having on engagement is relatively low, and we’re really pleased with how low that is,” he said. “Over time, we’ve shipped a number of changes to our algorithm that may cause content to go up or down.”

Facebook said in a statement that “the median amount of feedback on posts (likes, comments, shares) from people who have more than 10,000 subscribers is up 34 percent from a year ago.” But Facebook has also said that there has been a 2 percent drop in interaction on the news feed, and is now replacing free content with paid content, which means a large number of free posts will disappear from people’s feeds as sponsored ads float to the top.

Eben Moglen, a professor at Columbia who specializes in Internet law, said that although Facebook’s decisions to prioritize paid content could be seen as unethical, the company is not breaking any antitrust laws, yet.

“While the effort that is being characterized is problematic, no one has defined Facebook as dominant in a market,” he said, adding that the competition among social networks leaves it open to operate of its own devices.

In the past, lawmakers have gone after big companies that favor their own products and suppress others.

Microsoft in the late 1990s took advantage of its hold on PCs to force Internet Explorer onto people. Recently, Google has caught the attention of the Federal Trade Commission and a number of European regulators for highlighting its own products in search results. But in both instances, the companies were monopolies. Although Facebook has one billion users, there are plenty of other social networks and billions of people still not on the site.

“Certainly Facebook has changed its policies and adjusted its products in order to squeeze as much revenue out of all of the openings of the business model in a way that they didn’t have to do before they went public,” said James McQuivey, an analyst at Forrester Research and author of the book “Digital Disruption.” “It’s very possible there’s now a giant pendulum swinging within Facebook, where every division is under pressure to find revenue and advertising solutions.”

But for those who use Facebook for business needs, like restaurants, news outlets and local mom-and-pop shops that rely on the site to update customers, the changes could be damaging.

“It’s not just that people will feel nickeled and dimed by this, it’s that ultimately the value of the product disappears as the stream of information in your social network, one that used to be rapid and friction-free, is no longer there and now consumed by advertising,” Mr. McQuivey said.

When I asked Avichal Garg, another product manager for Facebook’s news feed, why my interaction count dropped so sharply, he said the company clearly needed to improve its algorithm.

“It’s really not in our best interest to take out the most engaging stuff and replace it with ads,” he said. “We want to make sure we show the right content to the right people.” Facebook’s ability to control the algorithm puts it in a different position from its competitors.

Twitter has the same type of advertising module, the sponsored tweet, but although it might highlight the ad in a user’s stream, it does not suppress other people’s content in the process. Everything just falls into a time-based stream.

Facebook may become dominant enough that its actions vex regulators, then it may be forced to change what it highlights. Or, maybe its users will grow so tired of what seems like another bait-and-switch that they will decide to stop sharing, even if it seems to be free.

E-mail: bilton@nytimes.com