The African National Congress says it will drag South African anti-corruption investigators to parliament, accusing them of smearing MPs.
The ANC has previously clashed with the Scorpions
ANC chief whip Mbulelo Goniwe said the Scorpions had tried to make MPs look like "cowboys and crooks".
The Scorpions are investigating an alleged $2m scam, in which MPs are accused of hugely inflating their travel expenses.
The opposition said the ANC was trying to "obscure the culpability" of MPs.
The Scorpions had said that 40 current and former MPs would be charged last week but none has yet appeared in court.
Mr Goniwe said that Scorpions press statements came out at the same time as state occasions, such as President Thabo Mbeki's State of the Nation address.
"I don't think it is a coincidence. I think it's a planned, desperate kind of act of vengeance to really undermine parliament and create this impression that members of parliament are by definition cowboys and crooks," he said.
Several high-profile MPs could face criminal charges
The accusations were dismissed by the Scorpions - a division of the National Prosecuting Authority.
"Quite frankly it [the comments] does not warrant a response," National Prosecuting Authority spokesperson Makhosini Nkosi said.
The police previously told the parliamentary speaker that those being investigated were members of the ANC and two opposition parties.
Charges have been expected since last August, when a report from an accountancy firm was handed to parliament.
The ANC previously clashed with the Scorpions over corruption allegations made against Deputy President Jacob Zuma.
Former Scorpions head Bulelani Ngcuka was criticised for saying he had some evidence against Mr Zuma but not enough to prosecute.
The travel scam involves the use of fake airline tickets and illegal claims for nights in luxury hotels worth $2m.
Politicians regularly have to travel from their constituencies throughout the country to parliament in Cape Town.
For this they are given travel vouchers for economy class flights.
But it is alleged that these travel arrangements were abused, with politicians using the vouchers for example to fly friends and relatives around South Africa.