As Microsoft prepares to launch its new chat app on Wednesday, Slack has a message for the company – and it took a full page in The New York Times to send it.

Slack bought a full page ad in Wednesday’s New York Times to publish an open letter to Microsoft about the impending launch of its new app, which will compete directly with Slack.

Slack CEO Stewart Butterfield posted a photo of the company’s letter to Microsoft on his Twitter account:

The letter was also posted on Slack's blog and begins with a word of congratulations for Microsoft:

"Wow. Big news! Congratulations on today's announcements. We're genuinely excited to have some competition.

"We realized a few years ago that the value of switching to Slack was so obvious and the advantages so overwhelming that every business would be using Slack, or 'something just like it,' within the decade. It's validating to see you've come around to the same way of thinking. And even though - being honest here - it's a little scary, we know it will bring a better future forward faster.

"However, all this is harder than it looks. So, as you set out to build 'something just like it,' we want to give you some friendly advice."

The letter goes on to say that "Slack is here to stay" and welcomes Microsoft "to the revolution":

"We're glad you're going to be helping us define this new product category. We admire many of your achievements and know you'll be a worthy competitor. We're sure you're going to come up with a couple of new ideas on your own too. And we'll be right there, ready."

According to recent reports, Microsoft was considering an $8 billion bid for Slack, but Microsoft founder Bill Gates and current CEO Satya Nadella opposed the deal in favor of developing an in-house solution, before an offer could be made.

Now Microsoft is launching its work-chat app called Teams, a chat app that - much like Slack - offers "channels," which are different chat rooms that work teams can set up for themselves. A video introducing Teams is now up online:

The Slack ad appears to be a riff on an Apple ad from 1981 welcoming IBM to the personal-computer market and reminding the company that Apple was there first. That ad ran as a full page in The Wall Street Journal. And even that ad apparently channeled one from an early IBM competitor, Data General, after IBM entered the minicomputer industry.