Hold on, didn’t Salesforce complete its $15.7 billion acquisition of Tableau Software? Not just announce it, but complete it?

It’s understandable to react that way if you’ve been following the story of the San Francisco-based cloud giant’s purchase of the Seattle-based data visualization technology company.

Yes, it’s true, as announced by the companies on Aug. 1, Salesforce completed the largest acquisition in its history, making Tableau its wholly owned subsidiary. Tableau is no longer a standalone company, its stock has stopped trading on the New York Stock Exchange, and Salesforce is incorporating the Seattle company’s revenue expectations into its own financial projections.

But more than two months after the deal closed, an ongoing review by the UK’s antitrust regulator is preventing the companies from integrating. An order from the UK’s Competition & Markets Authority (CMA) requires Salesforce and Tableau to keep their operations separate while it examines the merger to determine if it will substantially reduce competition.

In effect, the order applies broadly to the global operations of the companies. The order restricts their ability to share confidential financial information, work together to pursue customers, combine their brands, shift executives between the companies, or pretty much anything else that would normally be expected at this stage, without special permission.

The deadline for an initial decision is Nov. 29, based on the standard timeline laid out by the relevant statutes, but the CMA cautions that there’s no guarantee the timeline won’t be pushed back.

Beyond putting a temporary hold on their integration, it’s not yet clear how the review might impact the companies. Because the acquisition has technically been completed, it would be difficult to unwind completely, requiring a new transaction, sale or spinoff to make Tableau a completely separate company again. With the deal done, it can’t be spoiled by competing bidders, and any regulatory remedy is more likely to put restrictions on business operations or perhaps require smaller asset divestitures.

The timing is especially tricky given that both Salesforce and Tableau are preparing to host their big annual conferences next month, Dreamforce and the Tableau Conference, without knowing if they can attend each other’s events without restriction, let alone give their respective customers a clearer sense for what the acquisition will mean for their products and technologies.

For representatives of Tableau to attend an earlier Salesforce conference, the companies needed to get consent from the CMA, which restricted the information attendees could share with each other on site, requiring that all attendees be given a warning about “the importance of ensuring that no confidential information is exchanged during the conference.”

(Details of that conference were redacted in the public filing, but the file name on the Aug. 2 order indicates that it was in Hawaii, which isn’t a surprise given that it was a Salesforce event. This continues the companies’ tradition of inadvertently disclosing minor secrets through document file names; GeekWire previously deduced that Salesforce and Tableau conducted their merger talks under the secret code name, “Project Tiburon.”)

After the companies received special permission from UK authorities to share some financial information, Salesforce did gain more visibility into Tableau’s finances. In its Aug. 22 quarterly report, Salesforce raised its revenue guidance for its current fiscal year to a range of $16.75 billion to $16.90 billion, which included approximately $550 million to $600 million of revenue from Tableau, the company said at the time.

With so much at stake, and thousands of employees and customers impacted, you can imagine the consternation this is causing for people inside both companies. But they’re both playing it straight and abiding by the rules laid out by the UK competition authority.

Responding to a GeekWire inquiry this week, Tableau confirmed that the merger has closed and said it’s “continuing to fully cooperate with the CMA” but couldn’t comment on active regulatory matters. Salesforce declined to comment. In regulatory filings, the companies have promised to “remain operationally separate” while the review is pending.

We’ve contacted CMA representatives seeking updates on the nature and timing of the review. Failure by the companies to comply would give the CMA the authority to impose penalties of up to 5 percent of global turnover, or revenue, or as much as $800 million based on Salesforce’s financial projections.

Even after the integration of the companies proceeds, Tableau is expected to remain based in Seattle and continue to operate under its own brand, led by Tableau CEO Adam Selipsky, a former Amazon Web Services executive.

Salesforce, which has expanded in recent years beyond its core customer relationship management technology into cloud services, business applications and artificial intelligence, is looking to move further into business intelligence by leveraging Tableau’s technology for creating charts, graphs and detailed visualizations from large data sets. The deal escalates the competition between Salesforce and Microsoft, which competes with Tableau through its PowerBI technology.

Tableau employs more than 4,200 people worldwide, about half of them in the Seattle region. Salesforce employs more than 1,000 people in the Seattle region, part of a global employee base of 35,000 people. Marc Benioff, Salesforce co-founder and co-CEO, said when the deal was announced that it would effectively make Seattle the company’s second headquarters.