Deputy tax minister Folkert Idsinga is under pressure to publish details of his €6 million investment portfolio after a majority of MPs backed calls for full disclosure.

Idsinga, a former VVD MP who joined Pieter Omtzigt’s NSC party last year, declined to reveal which companies he held shares and other financial interests in, claiming it was a “private matter”.

On Tuesday Geert Wilders, whose PVV party is the largest in the coalition, added his voice to those demanding a breakdown of the minister’s financial affairs.

“This doesn’t look like good governance or a solid justification to me,” Wilders posted on social media site X.

Wilders’ words were a direct reference to NSC’s election campaign pledge to create a more robust, transparent system of government where MPs are more accountable to parliament.

The two coalition partners were locked in a stand-off for weeks over Wilders’s plans to use emergency powers to introduce more stringent asylum rules, while NSC wanted to pass a regular law through the fast-track procedure so that parliament can scrutinise and vote on the measures.

Wilders last week abandoned the emergency powers route, which faced strong opposition in the Senate and was almost certain to be challenged in the courts, but the measures themselves, such as border checks and detention for failed asylum seekers, remained intact.

Conflict of interest?

Idsinga he had discussed his interests during the formation of the cabinet and put his businesses “at arms’ length” when he accepted the post of minister for tax affairs and the tax administration (Belastingdienst).

“In concrete terms that means that during my period of office I have no recourse to or authority over [my investments] and that – where relevant – other people have been mandated to exercise my voting rights,” he said.

But opposition parties including GroenLinks-PvdA, D66 and the Socialist Party (SP) said Idsinga should release the full details of his financial holdings to ensure there was no conflict of interest.

“Where is the good governance of NSC?” SP leader Jimmy Dijk asked, adding that MPs needed to know if the minister was taking decisions in the national interest or his own.

Idsinga told RTL Nieuws, who published the original story based on the annual report of his financial holding company, that he supported transparency in government.

“But there is such a thing as people’s private lives,” he said. “I do my best to be as transparent as possible within the rules as stated and I don’t see why I should go any further than that.”