AMSTERDAM, March 29 (Reuters) - Dutch mail and packages company PostNL on Tuesday said that two of its nine hubs in Belgium remain closed after police raids as part of an ongoing investigation into labour practices.

Belgium's Minister for Public Enterprises said in a statement that it appeared from the raids, in which several people were arrested, that "infringements may have been committed".

"I cannot and do not wish to comment on the case itself, it is up to the courts to do their job," Petra De Sutter's statement said, adding that all postal operators in Belgium should offer their workers permanent contracts.

PostNL disclosed in its 2021 annual report that the Belgian labour inspectorate had found the company in breach of employment regulations -- including allegedly treating delivery workers as freelancers -- and local authorities would press charges.

PostNL denies any wrongdoing.

Two hubs were raided by police on Monday and remained shut on Tuesday, said PostNL spokesperson Jochem van de Laarschot.

"Because there is no official information [about the reason for the raids], it's hard to defend yourself," he said.

He could not confirm a report by Belgian newspaper Het Laatste Nieuws that the company's top executive in Belgium has been arrested.

However, Van de Laarschot said PostNL was aware that several of its Belgian employees were being questioned by police.

Most of the 1,400 workers who deliver PostNL packages in Belgium are employed by subcontractors, the company says.

The company reported 79 million euros ($88 million) in revenue from Belgium in 2021, out of a 3.47 billion euro total.

($1 = 0.8994 euros) (Reporting by Toby Sterling and Marine Strauss Editing by David Evans and David Goodman )