Joe Ricketts, CEO of the local news websites DNAinfo and Gothamist, announced Thursday that he is shutting down the digital publications. The sites and all of their past stories were taken offline.

The announcement came a week after the editorial staff voted to unionize with the Writers Guild of America East. The shutdown puts 115 people out of work, according to the New York Times.

In a letter to readers, Ricketts said in part: "Today, I've made the difficult decision to discontinue publishing DNAinfo and Gothamist. Reaching this decision wasn't easy, and it wasn't one that I made lightly."

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DNAinfo launched in 2009. It was an online publication that focused on neighborhood news in Chicago and New York City. Gothamist provided readers with coverage of news, culture, food and other local events.

In the letter, Ricketts praised the publications' success, noting their ability to reach millions of fans through social media and email newsletters. He said the publications together brought "over 15 million visits to our sites by over 9 million people" each month.

However, Ricketts, the billionaire founder of TD Ameritrade and owner of the Chicago Cubs, said the business was not sustainable.

"DNAinfo is, at the end of the day, a business, and businesses need to be economically successful if they are to endure. And while we made important progress toward building DNAinfo into a successful business, in the end, that progress hasn't been sufficient to support the tremendous effort and expense needed to produce the type of journalism on which the company was founded," he wrote.

"I'm hopeful that in time, someone will crack the code on a business that can support exceptional neighborhood storytelling for I believe telling those stories remains essential."

DNAinfo and Gothamist reporters took to Twitter to lament not just the loss of their jobs, but the disappearance of years of published work.

"We were the best in the game and I can't put into words what a loss this is to NYC news," Brooklyn reporter Noah Hurowitz wrote. "I have bled, sweat, cried, put myself in harm's way for this job, and now the last two years of my live have been erased."

He also leveled the charge that the shutdown was "direct retaliation" for the staff voting to unionize.

This is an act of direct retaliation for our successful union effort. I have no regrets. We did the right thing, stood tall. I am proud — Noah Hurowitz (@NoahHurowitz) November 2, 2017

Ricketts' letter made no mention of the unionization campaign, which he had fought. The New York Times reports that when the workers tried to organize last spring, he told them, "As long as it's my money that's paying for everything, I intend to be the one making the decisions about the direction of the business."

The Writers Guild of America East issued a statement saying it was "deeply concerned" by the shutdown. "The New York offices of DNAinfo and Gothamist recently voted to unionize and it is no secret that threats were made to these workers during the organizing drive," the union said. It pledged to "aggressively pursue our new members rights."