Palantir Technologies, one of the most valuable startups in Silicon Valley, has deprived investors of basic information about its business and repeatedly hindered efforts by investors to sell their shares, according to a blistering lawsuit filed by a longtime investor.

In addition to keeping at least some shareholders in the dark about its financial performance, Palantir has “engaged in a pattern and practice” of attempting to thwart their attempts to sell stock, according to the lawsuit, filed by investment firm KT4 Partners. Instead of letting these investors sell shares, Palantir has steered their sale opportunities to itself or its executives, while showering a favored brokerage firm with commissions even when the firm does no work at all, the lawsuit claims.

KT4 Partners first bought Palantir shares over a decade ago and is seeking to compel Palantir to hand over financial records, which it says are needed to understand the value of its investment. Further, KT4 claims it needs this information to investigate whether Palantir or its executives have engaged in “improper and illegal conduct” to harm minority shareholders. The lawsuit was filed under seal last week in the Delaware Court of Chancery; a partially redacted version was released on Monday and is reported here for the first time.

Palantir, in an emailed statement, referred to an earlier lawsuit that it filed against Marc Abramowitz, the managing member of KT4, claiming he stole Palantir’s intellectual property (a claim KT4 says is “meritless”).

“This lawsuit is nothing more than a blatant attempt to distract from Mr. Abramowitz’s unlawful and egregious theft of our intellectual property,” Lisa Gordon, a Palantir spokesperson, said in the statement. “His allegations are without merit and needless to say, Palantir will continue to aggressively pursue its existing legal action against him.”

Co-founded in 2004 by the billionaire Peter Thiel, who is now advising President Donald Trump, Palantir analyzes data for government agencies and major corporations. It has a $20 billion valuation, making it the third most highly valued startup in Silicon Valley, behind only Uber and Airbnb. Yet Palantir — whose stock changes hands only through private trades — goes to great lengths to keep any detailed information about its business private. A report by BuzzFeed News last year gave an unprecedented, though limited, account of its commercial operations.

The lawsuit, a highly unusual step for a startup investor, follows efforts by KT4 to obtain business information through other means. KT4 made a written demand last August to inspect Palantir’s books and records, the lawsuit says. But then, according to the lawsuit, Palantir retroactively amended its investors’ rights agreement “for the sole and express purpose” of avoiding disclosure obligations.

In September, Palantir filed its lawsuit against Abramowitz — which, according to KT4, has the “true purpose” of preventing disclosure of information and intimidating the investor. Palantir, in the lawsuit, described Abramowitz as a onetime confidant to Palantir executives who betrayed their trust.

Palantir is under increasing pressure from its shareholders, a number of whom have held its stock for a decade or more and are anxiously awaiting a payday. Former employees, who received a major part of their pay in stock options, have struggled to cash out, despite limited share purchase offers arranged by the company. Last fall, in a reversal of his longtime refusal to pursue an IPO, Palantir CEO Alex Karp said at a tech conference, “We’re now positioning the company so we could go public.”

This statement by Karp has a previously undisclosed backstory, according to the lawsuit: KT4 says it came after a formal request by the investor for information on whether Palantir had considered an IPO.

KT4 says its stake in Palantir is worth over $60 million — a significant sum by many measures, but small in the context of Palantir, which has raised more than $2 billion from investors. When KT4 tried to sell portions of its stake, Palantir repeatedly interfered, the lawsuit claims. Palantir, following a common practice in Silicon Valley, requires that any sellers of its stock seek the company’s approval for the transaction; companies do this to limit and manage ownership of their shares.

But remarkably, KT4 claims that when Palantir receives information from an investor about a planned sale, it uses that information to contact the buyer and persuade them instead to buy shares directly from the company or from certain Palantir insiders. One particular broker, Disruptive Technology Advisers, or DTA, repeatedly gets commissions from these sales, even when it “performed no legitimate work,” KT4 claims.

KT4 says it experienced interference by Palantir when it tried to sell shares to Highbridge Capital Management, a hedge fund that was owned by JPMorgan Chase, in May 2015. After KT4 notified Palantir of the planned sale, Palantir turned around and instructed DTA to “take the opportunity, on Palantir’s behalf,” and arrange a sale from Palantir to Highbridge instead, according to the lawsuit.

But when Alex Fishman, a founder of DTA, met with a senior managing director at Highbridge, the hedge fund executive said he would not break his deal with KT4, telling Fishman to leave his office, according to the lawsuit. The situation escalated when Karp, the Palantir CEO, learned of Highbridge’s affiliation with JPMorgan — a very important customer of Palantir’s — and that the bank’s CEO, Jamie Dimon, “would be asked to contact Karp directly to express displeasure” at these tactics, the lawsuit says. Karp then allegedly let the sale by KT4 go through.

Later, in December 2015, Palantir and DTA had more success in impeding a sale of shares by KT4 and other investors to a Chinese investment company, whose name is redacted in the document, the lawsuit says. DTA, representing Palantir, contacted the buyer and led it to believe that it was required to buy the shares directly from Palantir, ultimately leading the buyer to call off the deal with KT4 and the others.

Until KT4 made its recent demand for financial information, Palantir refused to provide financial information to buyers of its shares except through DTA — forcing buyers and sellers to do business with that firm or with Fishman, the lawsuit says.

Even when DTA was not involved in a deal, it still could get paid, according to KT4. Last summer, when UBS Securities was brokering a sale of Palantir shares, Karp demanded that UBS pay 25 cents a share to Fishman and DTA, even though DTA “had performed no work on the transaction” — and UBS agreed to make the payment, the lawsuit says. (KT4 says it learned this from a UBS managing director, but in an interview with BuzzFeed News, a person close to UBS disputed that the bank participated in such a sale and denied that UBS agreed to pay DTA.)

Fishman and Alex Davis, the other DTA founder, recently “enjoyed a very close relationship” with Karp, according to the lawsuit. (According to Fishman’s LinkedIn profile, he sold his half of DTA to Davis last week and no longer works there.)

Emails sent to Fishman and Davis were not immediately returned. Spokespeople for JPMorgan and UBS declined to comment.

Even as it blocks sales by smaller investors, Palantir has allowed Karp and Thiel to sell shares, according to the lawsuit. KT4 claims that these sales fly in the face of rights it has as an investor to participate in such transactions.

In addition to business data, KT4 says it is seeking information about the compensation and equity grants given to Palantir brass, to determine whether the company is spending on “lavish expenses” that serve no corporate purpose. KT4 says it has learned that Karp, the CEO, has “an unreasonably large number of executive assistants,” known inside Palantir as “Team Karp.”

In addition, KT4 claims it has learned that Palantir pays for someone or something — this part is, tantalizingly, redacted — to accompany Karp in the United States.

“There is no reason such [redacted] would be necessary or serve a valid corporate purpose,” the lawsuit says.