Since dawn on Tuesday 84 people have been brought into custody in Istanbul. The arrests are a culmination of a two year probe into allegations of corruption, money laundering, gold smuggling and bribery and have sent shock waves through Turkey.

The Financial Crimes Unit arrested high profile names including the sons of the economics, interior and urban planning ministers. The General Director of the state run lender Halkbank, the Mayor of Fatih district in Istanbul, Mustafa Demir and the construction mogul Ali Agaoglu, as well as several bureaucrats from the environment and economy ministries, have all been taken into custody.

The arrests have shone an uncomfortable light on the close relationship between the government and the construction industry just months before the elections in Spring. The opposition parties have today been calling for Erdogan’s resignation.

Three separate investigations started following tip-offs that high-level bureaucrats and the relatives of ministers were making profits from development schemes, and the complex relationship between the planning authorities and construction companies started to be untangled.

Before the scandal emerged, the government was proud of the rapid expansion of Istanbul’s metro system, most notably the Marmaray construction project, a metro that goes under the Bosphorus connecting Asia to Europe. When the tunnel was opened concerning reports emerged regarding the safety of the tunnel, and these concerns have grown following the arrest of the Mayor of Fatih, a municipality district in Istanbul.

A report was written by the Japanese engineers warning the municipality that the construction of a hotel next to the metro station could put the tunnel in danger. The Mayor, Mustafa Demir, is accused of accepting bribes to shelve this report and approve the construction license for a hotel in this location.

This strand of the investigation has revealed an illegal organisation supposedly led by an architect called Sevinc Dogan. The organisation stands accused of bribing public servants to acquire construction permits for historical areas in Istanbul and selling any historical artefacts found on these sites. This has been the case in three Istanbul municipalities; Fatih, Besiktas and Sariyer. Demir in particular is suspected in taking $1.5m for downgrading a first-degree historical region to a second-degree to allow building projects on these sites.

Another crime ring was also unearthed by this strand of the investigation. Yesterday Abdullah Oguz Bayraktar was accused of establishing a crime ring and accepting bribes from construction companies in return for construction permits. Twenty-two of those detained yesterday are part of this particular investigation.

These arrests show the scale of the corruption. Individuals have been profiting from abusing the authority of the Ministry of Environment and Urban Planning to sidestep the laws surrounding protected areas. These SIT areas are pieces of land designated for local municipalities, but following bribes they were opened for construction.

Photos taken after the raid of the son of the Interior Minister’s house show six safe boxes full of US dollars and Euros were released by the Daily Radikal today.

A large amount of money was also reportedly discovered in a number of shoeboxes at the home of Suleyman Aslan, the General Manager of Halkbank. $4.5 million was reportedly confiscated from his home by police this morning. This is part of another investigation which focused on businessman Reza Zarrab and the Halkbank, a state run lender.

Zarrab has a history of Iran-related crimes. Earlier this year his residence was raided and 27kg of gold belonging to him was seized at Atakurk Airport. It is suspected that the gold was intended for his jewellery stores in Iran.

Yesterday, however, Zarrab was arrested on allegations that he runs a crime ring. He is accused of paying bribes to cabinet members to cover up ‘suspicious’ money transactions and bribing bureaucrats to acquire Turkish citizenship for relatives and friends. The money transfers involve sending money to Iran via the state run lender Halkbank. Yesterday the offices of Halkbank were raided and shares in the organisation fell 5%.

Like Zarrab, Halkbank is no stranger to controversy. In 2012 the bank was suspected of facilitating an exchange with Iran, 60 tonnes of gold for several million tonnes of crude oil, despite the international trade sanctions imposed on the country. In April this year local media reported that 47 members of the US Senate had demanded sanctions on Halkbank, and the bank had to release a statement denying accusations that it was carrying out activities which broke the international trade sanctions with Iran.

So far there has been little word from the Erdogan government. A spokesperson from the government Huseyin Celik, called for the attention to be paid to the presumption of innocence of those taken into custody because “in a state of law everybody is equal before the law.”

However, the main opposition, the Republican People’s Party (CHP), have called on the Prime Minister to resign, with the CHP Deputy Parliamentary Group Chair Engin Altay saying:

“This is the biggest scandal in the Republic’s history. The Prime Minister should resign.”

The Deputy Group Leader of the National Movement Party (MHP), Oktay Vural, has also reacted strongly to the arrests, saying that the Ministers whose sons have been taken into custody should not continue in their duties, and noting that: