Amnesty International says a proposed amendment to Iran's Criminal Code could deny individuals access to a lawyer while they are under investigation and facing serious charges.

Iran's parliament is expected to vote on the proposed amendment in the coming weeks.

If approved by lawmakers, it would be a "crushing blow to Iran’s already deeply defective justice system," the rights watchdog said in a statement released on May 16.

The amendment would allow the prosecution to instantly deny individuals access to a lawyer if they are arrested on "national security" charges and other serious criminal accusations. Initially access would be denied for 20 days, which could then be prolonged to cover the entire investigation.

Dozens of human rights activists, independent journalists, and political dissidents have been facing national security charges.

"This is a regressive piece of draft legislation which would effectively remove the right to a lawyer in a wide range of criminal investigations and contravene Iran's obligations under international law," said Philip Luther, research and advocacy director for the Middle East and North Africa at ‎Amnesty International.

Luther added that the move could "further consolidate patterns of torture and other ill-treatment against detainees to extract forced confessions during interrogations," and said the denial of access to lawyer is a "serious violation of the right to a fair trial."

The watchdog said Iranian authorities have for decades failed to ensure that the right to access a lawyer is respected.