Four Republican lawmakers called Thursday for a delay in implementing a plan to cede US oversight of the internet address system, saying it could give more power to "authoritarian regimes."

The lawmakers said they have concerns over the plan to turn over to the broader online community oversight of the Internet Corporation for Assigned Names and Numbers (ICANN), set to take place October 1.

The handover represents "a serious, groundbreaking, and potentially unalterable action," said the four, each of whom chairs a key committee: Senators John Thune of South Dakota and Chuck Grassley of Iowa and Representatives Fred Upton of Michigan and Bob Goodlatte of Virginia.

In a letter to US Attorney General Loretta Lynch and Commerce Secretary Penny Pritzker, the lawmakers said they had "examined the arguments for and against the proposed transition, including concerns about whether the transition could enhance the role of authoritarian regimes in internet governance."

They said witnesses at hearings have identified "concerns that important accountability measures have yet to be fully fleshed out, tested, or proven."

Earlier this year, ICANN said it had worked out details of the plan that removes the symbolic US government oversight of the internet address system.

US officials in June gave tentative approval to the plan, which enables a broad range of internet "stakeholders" to make policy and avoids direct government management of the internet.

In August, officials said the US government contract with ICANN would expire as scheduled on September 30.

Officials have said the plan to "privatize" this system has been in the works for some 18 years and would instill greater confidence in the independence of the internet from the US government.

Some critics of the plan have argued that it would leave the internet accountable to no one and enable repressive regimes to exercise more control.

"There is a broad range of important questions on both law and policy that remain outstanding with respect to the proposed transfer," the Republican lawmakers wrote.