Green MP Caroline Lucas has questioned whether a donation to the Conservatives made by a minicab firm owner is behind changes to Taxi and private hire regulations.
She told a debate in Parliament that a £500,000 donation made by Addison Lee chairman John Griffin may have influenced the government's policy.
Annual checks on minicab licence holders are to be replaced with reviews every three years under ministers' plans.
But Addison Lee "categorically" denied any attempts to influence legislation.
And a spokesperson for the Department for Transport said: "This is a bizarre claim, perhaps based on a misunderstanding of the proposals, which apply only to Taxi and private hire services outside London.
"They would therefore have no impact on Addison Lee's operations, which are within London.
"We believe our proposals will have a discernable and beneficial effect on the Taxi and private hire trade and for passengers."
But a spokeswoman for Ms Lucas responded that Addison Lee bosses had told the Evening Standard in 2013 that they were keen to expand the firm to other cities in the UK, so there was nothing "bizarre" about suggesting that deregulation of minicab firms outside London was in their interests.
Ministers have pre-empted a review of Taxi and private hire regulations by the Law Commission and included the changes to Taxi and private hire regulation in the Deregulation Bill currently being considered by Parliament.
Speaking in Westminster Hall, the Commons' secondary debating chamber, Ms Lucas said questions needed to be asked about why such "potentially dangerous" changes were being "rushed through".
And she questioned the role played by Addison Lee and its chairman John Griffin.
"We know there's good money to be made from the taxi and private hire vehicle or minicab industry," she said.
Mr Griffin gave £500,000 to the Conservatives in 2013.
"Addison Lee have made so much money, they're actually giving it away in large quantities to the Conservative Party."
"Are we really supposed to believe that Addison Lee has had no influence on the move to push amendments through before the publication of the Law Commission's in depth review?"
Mr Griffin, she claimed, was "clearly a man with a potential political agenda".
"I think we cannot help but ask ourselves what might he want back in return for his large donation."
Mr Griffin donated £500,000 to the Conservatives in July 2013 while Addison Lee donated £254,045 to the party between December 2008 and September 2011.
Addison Lee said Mr Griffin had made his donations to the Conservatives "in a personal capacity".
"Whilst Addison Lee believes a review of the current UK taxi and private hire laws is long overdue, we can categorically confirm that none of our staff or directors has attempted to influence any early amendments to this legislation," a spokesman for the firm said.
"We welcome the chance to have our say when the Law Commission publishes its review."
Changes proposed in the Deregulation Bill include a ban on ordinary licence holders driving a private hire vehicle when it is off-duty, while firms will be able to subcontract work in future.
The Law Commission is taking submissions on changes to the regulation of the industry, which were intended to be brought to Parliament in a separate bill.
Transport Minister Stephen Hammond told MPs the decision to include new laws in the Deregulation Bill was "pragmatic" and would allow "immediate progress" to be made.