NEW YORK >> Two popular New York City news sites and their satellites in Chicago, San Francisco and elsewhere were shut down a week after their New York staffs voted to unionize.

Joe Ricketts, the billionaire CEO of DNAinfo and founder and former chief executive of what is now TD Ameritrade, said in a post on the site Thursday that the decision was due to business reasons, although he has previously been outspoken against unions.

“Businesses need to be economically successful if they are to endure,” he said. “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.”

Late last week, the editorial staffs of the New York outlets voted to unionize with the Writers Guild of America, East, AFL-CIO. The companion staffs in Chicago, Los Angeles, San Francisco and Washington did not, although they all were apparently shut down on Thursday. A total of 115 journalists will be out of work as a result, according to the New York Times.

A guild spokesman said the union is “deeply concerned” about the decision.

“It is no secret that threats were made to these workers during the organizing drive,” spokesman Jason Gordon said. “The Guild will be looking at all of our potential areas of recourse and we will aggressively pursue our new members’ rights. We will meet with management in the near future to address all of these issues. We are currently working with the staff at DNAinfo and Gothamist to support them in this difficult time.”

Ricketts also is the owner of the Chicago Cubs. He founded DNAinfo in 2009 and bought Gothamist earlier this year. He did not mention the union vote in his statement Thursday, but previously posted a commentary on his personal blog titled, “Why I’m Against Unions At Businesses I Create.”

He said in the commentary that “unions promote a corrosive us-against-them dynamic that destroys the esprit de corps businesses need to succeed. And that corrosive dynamic makes no sense in my mind where an entrepreneur is staking his capital on a business that is providing jobs and promoting innovation.”

A spokeswoman for Ricketts did not immediately respond to requests for comment.

Unlike DNAinfo, which was more shoe-leather news, Gothamist offered quirky takes on New York City life, from news to restaurant reviews to to-do guides. It had a lively comments section and sister sites such as SFist in San Francisco, Chicagoist and LAist in Los Angeles.

Ricketts’ statement noted that DNAinfo and Gothamist daily news reports were sent to a half-million email inboxes.