Parliament's plans to review the Protection of State Information Bill in two days makes a mockery of its duty to correct the contentious draft law, the Right2Know campaign said on Tuesday.

The lobby group said President Jacob Zuma had rightly referred the official secrets bill back to the National Assembly on advice that it was unconstitutional, but that the problems were too severe to be fixed by the deadline of Thursday.

"All MPs now have an important opportunity to fix the problems with the secrecy bill's constitutionality," Right 2 Know spokesperson Murray Hunter said.

"However, if Parliament believes this job can be done in two days, it confirms fears that the decision to refer the secrecy bill back to Parliament was only a delaying tactic.

"South Africa cannot accept a process that does not fix these problems, but instead aims to make small, cosmetic changes to a seriously flawed law."

Last month, Zuma sent the bill back to the legislature, saying it was incoherent and therefore unconstitutional, and pointing to two clauses in particular.

But opposition parties and activists said the wording of his letter to Parliament was too vague, and have urged him to say whether MPs had the authority to undertake a comprehensive redraft.

The president has remained silent on the issue and has failed to respond to a written request by the Democratic Alliance for clarity.

Critics' hopes for a comprehensive overhaul dimmed last week when Parliament scheduled the ad hoc committee handling the review to meet on Wednesday and to finalise its report on the bill on Thursday.

Hunter said this process would be a sham unless Zuma explained why he thought the bill was unconstitutional, and allowed MPs to thoroughly deal with remaining concerns.

"Until the president provides detailed information on his decision, any attempt to finalise the secrecy bill would be absurd," he said.

"The president must provide a full explanation of his decision not to sign the secrecy bill into law: does President Zuma share the concerns of so many people that the bill is an unconstitutional restriction of the right to access and share information?"

The bill's most hawkish provisions were watered down during three years on the drawing board, but critics say it still creates the spectre of excessive state secrecy reminiscent of the apartheid era.

The two clauses mentioned by Zuma when he announced his decision contain technical errors that, if corrected this week, are unlikely to alter the content of the bill and allay those concerns.