A federal judge ordered Elon Musk to testify again in the U.S. Securities and Exchange Commission’s probe of his $44 billion takeover of Twitter, giving the regulator and the billionaire a week to agree on a date and location for the interview.

U.S. Magistrate Judge Laurel Beeler’s order, issued on Saturday night, formalized a tentative ruling she made in December that sided with the regulator.

The SEC sued Musk in October to compel the Tesla and SpaceX CEO to testify as part of an investigation into his 2022 purchase of Twitter, the social media giant that he subsequently renamed X. Musk refused to attend an interview in September that was part of the probe, the SEC said.

The agency is examining whether Musk followed the law when filing the required paperwork about his purchases of Twitter stock, and whether his statements in relation to the deal were misleading.

Musk fought the SEC’s bid to interview him, saying it had already done so twice, and accused the regulator of harassment.

Beeler rejected that argument. The SEC had authority to issue the subpoena, which sought relevant information, she said in the ruling.

If the SEC and Musk cannot agree on a date and time for the interview, Beeler said she will hear from both sides and decide for them.

Friction between Musk and the SEC began when the regulator sued him after he tweeted “funding secured” in 2018 in reference to a possible plan to take Tesla private. To settle that case, Musk agreed that a Tesla lawyer would vet his tweets about the electric vehicle maker. The SEC sued him again in 2019 for allegedly breaching that provision.

Musk has asked the U.S. Supreme Court to review the agreement, saying it violates his constitutional right to free speech.