Writers trying to embed tweets in their Substack stories are in for a rude surprise: after pasting a link to the site, a message pops up saying that “Twitter has unexpectedly restricted access to embedding tweets in Substack posts” and explaining that the company is working on a fix.

After those reports surfaced, between Thursday night and Friday morning, Twitter apparently began to restrict promotion and visibility for tweets with links to Substack posts. New tweets linking directly to Substack.com can still be tweeted, but trying to retweet or like those tweets via Twitter’s website results in an error message saying, “Some actions on this Tweet have been disabled by Twitter,” while doing the same from within its apps or TweetDeck appears to work while failing silently.

The founders of Substack Chris Best, Hamish McKenzie, and Jairaj Seth, provided the following statement to The Verge in response:

We’re disappointed that Twitter has chosen to restrict writers’ ability to share their work. Writers deserve the freedom to share links to Substack or anywhere else. This abrupt change is a reminder of why writers deserve a model that puts them in charge, that rewards great work with money, and that protects the free press and free speech. Their livelihoods should not be tied to platforms where they don’t own their relationship with their audience, and where the rules can change on a whim.

Trying to reply to a tweet with a Substack link causes a different error, which reads, “Something went wrong, but don’t fret — let’s give it another shot.” There are some new tweets we’ve found linking to Substacks that don’t display this error, but it appears several authors have begun working around the issue by obscuring their links with redirect services like ShortURL to avoid the Twitter block.

The unfortunate situation comes on the heels of Substack announcing Notes, a Twitter competitor.

There are no public statements on the issue from Twitter or its owner / CEO Elon Musk; however, it’s a reminder of the day in mid-December when Twitter temporarily blocked links to all competitors, like Instagram, Facebook, and Mastodon. Before undoing the ban, Musk tweeted that “Twitter should be easy to use, but no more relentless free advertising of competitors. No traditional publisher allows this and neither will Twitter.”

The issue with embedding tweets in Substack posts could cause problems for writers who want to talk about what’s going on with Twitter in their newsletters or about things that are happening on the platform. While screenshots of tweets could work in some cases, they’re less trustworthy because they don’t provide a direct link to the source. Screenshots also won’t help you if you’re trying to, say, embed a video that someone posted on Twitter. (And Twitter seems to be at least somewhat interested in becoming a video platform, given that several Blue perks relate to making the video uploading experience better.)

As an example of how useful embedding tweets can be, here’s Substack’s official announcement that it’s looking into the issues:

When I asked Substack spokesperson Helen Tobin on Thursday about whether the issues with embedding tweets were caused by changes to Twitter’s API, she didn’t comment and instead shared the same statement tweeted by the company. If they are, though, it would be far from the only platform affected by Twitter’s new API policies, which were announced a week ago.

Since then, various companies have been notifying users that they have to cut out or paywall certain features that interacted with Twitter, and many people who have run bots on the platform have been posting about how they can no longer post like they used to. Here are some of the apps and bots that have been broken:

• Feedbin’s developer was told that the app “violated Twitter Rules and policies” by letting people access tweets in their RSS reader. Another RSS app, Inoreader, got the same message.
• TweetShift, a Discord bot that lets you interact with Twitter via the chat app, says it was “randomly suspended from the Twitter API” on Wednesday.
• TweeseCake and TWBlue, apps meant to make Twitter easier to use for blind users, are no longer working (at least on some platforms).
• Several novelty bots, such as gender of the day and Possum Every Hour, have warned users that they may no longer be able to continue posting.
• Botmaking tool Cheap Bots, Done Quick was suspended from the Twitter API, with its developer, V Buckenham, being told in an email to sign up for one of the company’s new API tiers. This will almost certainly bring down other bots that were made using the tool.

Buckenham told The Verge that the email was the only communication they’d received from Twitter about the suspension and that they hadn’t expected anything to change until the end of April based on the company’s statement that it’d be deprecating old accounts “over the next 30 days.” “I’ll confess I expected it to be a ratelimit, not the API key being revoked, though,” they said before adding, “But overall I’m not surprised to find Twitter’s changes rolling out unpredictably.”

Some developers have decried the new API plans as being prohibitively expensive. The “Basic” tier costs $100 a month and lets your app post a maximum of 50,000 tweets per month (with a 3,000 tweet per month limit per user) and read 10,000 tweets per month. There is a free tier, but it only lets you write tweets, not read them. That wouldn’t be useful for, say, the Thread Reader bot that makes strings of posts on the site easier to read.

The API transition has been bumpy, even for those that appear to be in Twitter’s good graces. Earlier this week, WordPress’ API access was suspended, making it so users couldn’t auto-share posts to the platform. The company was eventually able to get it restored and says that it’ll be “working with Twitter directly to ensure this service keeps running without interruption.”

There are several tools that integrate Twitter that do still work. Embeds still work in Ghost, a blogging platform similar to Substack, as well as in The Verge’s content management system (obviously). However, if those tools rely on API access to work, it’s possible there could be problems ahead as Twitter continues to depreciate access to it.

None of this will necessarily be a surprise to those who remember how Twitter treated third-party clients. In January, the company silently cut off their API access before rewriting its rules to ban them almost a week later.

Update 10:50AM ET:  Added details of Twitter blocking Substack links as well as workarounds.

Update 11:26AM ET:  Added response from Substack founders.