A Washington federal judge has set a showdown for Thursday between Humana and the Federal Trade Commission over whether the insurer will be forced to disclose documents the agency says it needs for its investigation of Walgreens Boots Alliance Inc.’s proposed $7 billion acquisition of Rite Aid Corp.

Humana pushed back against an FTC subpoena demanding documents the agency has said will help it “understand the competitive impact” of the Walgreens-Rite Aid tie-up.

Humana, represented by the law firm Wiley Rein, argued that the FTC was asking for irrelevant documents and that the agency’s demand would overly burden a company that is not directly involved in the Walgreens-Rite Aid deal.

The FTC is not backing down.

In a rare “emergency petition” on Monday, the agency asked a Washington federal judge to enforce the subpoena—a push that could signal the agency is gearing up to challenge Walgreens and Rite Aid’s merger plans.

U.S. Magistrate Judge G. Michael Harvey of the District of Columbia has set a hearing for Thursday afternoon. A lawyer for Humana, Wiley Rein partner Richard Smith, co-chairman of the firm’s litigation group, declined to comment Tuesday.

The FTC said it needs the Humana records by June 26, noting that Walgreens and Rite Aid could execute their deal—combining two of the three largest pharmacy chains in the country—as early as July 7.

“Between now and then,” the agency said, regulators must decide whether to challenge the deal as potentially anti-competitive. “As a result, time is of the essence,” FTC lawyers wrote. “Any delay in the resolution of the petition may limit the commission’s ability to conduct a comprehensive evaluation of the transaction,” the agency lawyers said.

“Humana’s unexplained refusal to comply with the commission’s subpoena hampers the commission’s ability to evaluate the proposed transaction and determine what action is in the public interest.”

The FTC’s document request related to Humana’s Medicare prescription drug plans, which feature Wal-Mart as the preferred in-network pharmacy.

The subpoena also demanded the company’s communications with the Centers for Medicare and Medicaid Services “on seven broad topics,” Humana said last month in a petition to limit the document requests.

Humana challenged the subpoena as “a quintessential example of a fishing expedition by the government for irrelevant documents, with the full cost of that expedition being foisted upon Humana, a non-party.”

“The subpoena is grossly overbroad, and many of the specifications are entirely unrelated to the FTC's investigation of the proposed acquisition,” Smith wrote in a filing on May 16 at the Federal Trade Commission. He added: “The costs that Humana, a non-party, will be forced to endure in an effort to isolate, collect, process, search for, review, and produce the documents demanded by the FTC are enormous, while the benefit to the FTC, if any, is paltry.”

Humana’s lawyers are going back to the same court they camped out in for weeks not so long ago. A judge in January granted a preliminary injunction blocking Aetna Inc.’s proposed acquisition of Humana, prompting the companies to abandon their merger plans.