Tate Modern art gallery in London needs to come clean about its financial ties to British oil company BP, advocates said Monday.

"There's a great deal of public debate surrounding Tate's longstanding relationship with BP, a company associated with a long list of environmental, human rights and climate controversies," Kevin Smith, an oil sponsorship campaigner from Platform, said in a statement.

Last week, more than 100 members of advocacy group Liberate Tate descended on the galleries of the Tate Modern in London to rally in response to a court ruling BP was "grossly negligent" in the events that led up to the 2010 spill in the Gulf of Mexico.

On Thursday, the gallery is scheduled to appear before a tribunal to answer questions related to how much money it receives from BP. The gallery gets less than 1 percent of its sponsorship directly from BP, though the advocates question the numbers available publicly.

Glen Tarman, an advocate who filed a Freedom of Information request against Tate, said gallery officials have worked to "censor" information about its "shady" relationship with BP.

There was no public statement from BP. Tate said it couldn't comment on ongoing proceedings.