The anti corruption group, Transparency International Papua New Guinea, says the government should have consulted widely with the people before making changes to the constitution.
Last month the Peter O'Neill government, which enjoys a huge parliamentary majority, amended the constitution to make it much more difficult for the opposition to bring votes of no confidence.
TIPNG executive director Lawrence Stephens says government concerns over stability would have been better served by MPs changing their behaviour.
He says when the constitution was drawn up there was widespread consultation and the same should apply to any changes.
"When it comes to changes the constitution, particularly something as dramatic as votes of no confidence, we would expect there to be widespread discussion and not this fast, almost hidden, approach to pushing legislation through."
Transparency International PNG's Lawrence Stephens.