South Africa's parliament is expected to pass a new state secrets law amid criticism that the measure will suppress the media and those exposing corruption.

Lawmakers are due to vote Tuesday on the bill backed by the ruling African National Congress party, which says the law is necessary to protect state secrets.

The measure would update apartheid-era provisions, and punish those who publish classified information with up to 25 years in jail.

Critics say the proposed law is extreme, and have argued for a clause that allows revealing state secrets in the public interest.

State Security Minister Siyabonga Cwele argued against a public interest clause last week, saying foreign spies are stealing information at the expense of South Africa.

The National Press Club has called on people to wear black on Tuesday to show opposition to the bill.