The government was using the first anniversary of the failed coup on 15 July 2016 to "write a fabricated history,” said Bulent Tezcan, a spokesman of the Republican People’s Party (CHP).
The government says it is cracking down to purge state institutions and prevent future threats.
But Mr Tezcan and his party call the state of emergency a "controlled coup” that must be revoked immediately.
Turkish president Recep Tayyip Erdogan addressed tens of thousands of people at memorial events in Istanbul and Ankara at the weekend. Accompanied by his family and the families of the victims of the coup, Mr Erdogan joined a massive, flag-waving crowd near the iconic July 15 Martyrs’ Bridge in Istanbul to remember 250 people who died on July 15 2016 resisting the coup.
Turkey blames US-based cleric Fethullah Gulen for orchestrating a violent attempt to overthrow of the government and the president but the cleric denies the allegations.
Mr Tezcan said inquiries were obstructed to protect the government which, he claimed, is using the state of emergency imposed after the failed coup to create a lawless environment without checks and balances.
"No investigations have been made into how this terror organisation got to such a daring point within the state, how it was placed there to attempt a coup, and new information was covered up,” he said.
The CHP MP said government pressure on the judiciary prevented prosecutors investigating the alleged infiltration of the coup plotters and their political connections.
He said a parliamentary investigation commission was used to fend off political accountability.
"The facts need to come out for the sacred memory of the 250 martyrs – those who died resisting the coup,” he said.
More than 50,000 people have been arrested and 110,000 public employees sacked for alleged links to Mr Gulen and other terror groups, under the state of emergency imposed on 20 July last year.
Mr Erdogan called the charge "rude and immoral” and accused CHP leader Kemal Kilicdaroglu of siding with Mr Gulen and other terror groups.
Mr Gulen was once an ally of the president but the two had a public falling out in 2013 and his movement was declared a terror organisation.
Mr Erdogan said the country was doing everything to punish the "traitors”.