Activists have covered a prized Picasso at the National Gallery of Victoria in a black veil to protest its contract with Wilson Security.

Activists are outraged that the artistic institution has a deal with the company involved in running the Manus Island and Nauru detention centres.

Around a dozen protesters covered the Weeping Woman in a cloth featuring Wilson's logo.

They stood in front of it to prevent security staff from removing it for around an hour, before leaving.

The group says the light veil was taped to the wall above the painting, and that there was no intention to damage the artwork or do any other harm.

The activists want the NGV to dump its contract with Wilson Security, a company that they accuse of covering up human rights abuses at the offshore detention centres.

They also penned an open letter to NGV director Tony Elwood in August, in which 1,500 artists, patrons and members of the public condemned the contract.

The opponents say the Wilson deal “sends a message endorsing the systematic abuse of vulnerable people”.

But Wilson Security was first given the contract after the NGV dumped the previous firms - Business Risks International – due to allegations it used subcontractors who underpaid staff and forced them to work for cash.

A gallery spokesperson said Wilson Security was an “interim” contractor.

“The NGV is currently in the process of securing a long-term security services provider, who will be selected and appointed through a public tender process as part of a revised Victorian Government security services panel later this year,” the gallery official said.

Wilson Security says it will leave the Manus Island and Nauru detention centres when its contract comes to an end, but has not commented on this particular protest.