The head of a US congressional committee probing LIV Golf’s proposed merger with the PGA Tour on Wednesday reiterated a demand for the governor of Saudi Arabia’s sovereign wealth fund to testify before lawmakers.

Richard Blumenthal, the US Senate Subcommittee on Investigations chairman, said in a letter to Yasir al-Rumayyan, the head of Saudia Arabia’s Public Investment Fund (PIF), that LIV should expect to be subjected to American oversight as an investor in the United States.

Al-Rumayyan has so far rebuffed requests to testify before the Senate panel, with attorneys for the Saudi official informing Blumenthal he was an “inappropriate witness” who should be exempt from testifying, citing his status as a Saudi government minister.

Blumenthal said in his letter released Wednesday that al-Rumayyan must agree to appear at a September 13 hearing or propose other possible dates to appear by Friday.

“If you continue to refuse to comply voluntarily the Subcommittee will be forced to consider other legal methods to compel PIF’s compliance,” Blumenthal warned.

LIV Golf and the PGA Tour rocked the sporting world in June after announcing plans for a de facto merger in a bid to end the acrimonious standoff between the two circuits.

However few details of how the new LIV-PGA entity will work have been revealed, other than that al-Rumayyan will get a seat among decision makers and PIF would invest in a for-profit company with the PGA Tour.

“PIF’s recent dealings with the PGA Tour demonstrate that it intends to be much more than a passive investor,” Blumenthal said.

Blumenthal also rejected al-Rumayyan’s reasoning for refusing to testify.

“The suggestion that your role as a Saudi Foreign Minister shields you from testifying about PIF’s commercial activities is both deeply troubling and unsupported as a legal matter,” Blumenthal said.

He also cited a US District Court ruling in California earlier this year that said PIF was not protected by “sovereign immunity” rules in its legal battle with the PGA Tour.

“PIF cannot have it both ways,” Blumenthal wrote. “If it wants to engage with the United States commercially, it must be subject to United States law and oversight. That oversight includes this subcommittee’s inquiry.”

Blumenthal also made it clear that another PIF representative appearing would not be enough to keep the subcommittee from wanting al-Rumayyan to appear at some stage.

“While the subcommittee will not accept a briefing from a PIF representative in lieu of your testimony and documents from PIF, it will accept a briefing from an appropriate PIF representative to learn more about PIF’s intentions while awaiting your testimony and document production,” he wrote.