Booking.com is facing renewed unrest over its pension obligations after the company said a court order to join industry fund PGB does not apply to all of its Dutch staff, the Financieele Dagblad reported on Tuesday.

In March, the Supreme Court ruled that Booking must participate in the travel sector pension scheme, rejecting its claim that it is a tech firm rather than a travel agency. The ruling forced the Amsterdam-based company to sign up to scheme and make back payments dating back to 1999, at an estimated cost of more than €400 million.

But Booking now argues that the obligation only covers employees of Booking.com BV, the entity directly named in the legal case, and not staff at other subsidiaries handling customer service, real estate or IT.

That would leave around 2,500 workers – about a third of its Dutch workforce – outside the travel industry pension fund, under a separate company scheme, the FD said.

The company’s interpretation has surprised the pension fund, which said it is investigating whether the other subsidiaries also fall under the mandatory sector-wide agreement. “If that is the case, they too will have to join,” a spokesman said.

Employees have voiced frustration about what they describe as “pension inequality,” the FD reported.

One worker told the newspaper the issue could even trigger strike action. Former works council member Gianluca Petruzzi has also gathered support on LinkedIn for a campaign to equalise pensions and is considering legal steps.

Booking, owned by US-based Booking Holdings, has long resisted being part of an industry fund, arguing that it needs “flexibility and autonomy” to set employment conditions to compete for international talent.

It is not the only platform company to clash with Dutch pension funds. Dutch courts have previously ruled against Deliveroo, Getir and Gorillas in similar disputes.