Top House and Senate lawmakers are engaged in a last-minute push to block the United States government from handing control of the Internet to a private, global organization.

Facing a Sept. 30 deadline, lawmakers opposed to the transition are lobbying the Obama administration to halt the move.

Sen. Ted Cruz, R-Texas, who is perhaps the staunchest congressional opponent to the handoff, said he is "cautiously optimistic" a rider prohibiting the transfer will be included in a must-pass government spending bill that is expected to become law by Sept. 30, the same date the transfer is supposed to take place.

Cruz this month delivered an impassioned speech denouncing the move, which would transfer control to a multi-stakeholder, nonprofit called the Internet Corporation for Assigned Names and Numbers, or ICANN.

"If the Obama administration hands control of the Internet over to this international organization, it's not like the next president can magically snap his or her fingers and bring it back," Cruz said. "Unscrambling those eggs may well not be possible."

The Obama administration has defended the move, which will involve transferring to ICANN the Internet domain name authority (IP addresses) now operated by the National Telecommunications & Information Administration.

Laurence Strickling, the NTIA administrator, said the transfer is necessary to ensure "that the private sector, not governments, takes the lead in setting the future direction of the Internet's domain name system."

Strickling added that the NTIA's stewardship "was intended to be temporary."

But Cruz and other critics have labeled the transfer an "Internet surrender," and say the ceding of U.S. control will allow more than 160 countries, including authoritarian regimes, to have some influence over what is allowed and prohibited on the Internet.

In other words, they argue, Internet freedom is threatened.

Cruz and Rep. Sean Duffy, R-Wisc., have introduced the Protecting Internet Freedom Act, which would prevent the Obama administration from transferring authority away from the United States.

Cruz held a hearing on the matter last week, inviting opponents and supporters of the plan to testify before a Judiciary subcommittee he chairs.

Cruz posed a question to ICANN's CEO and President Goran Marby that aimed to underscore his belief the transfer would truly threaten Internet freedom.

"Is ICANN bound by the First Amendment?" Cruz asked.

"To my understanding, no," Marby replied.

If Congress doesn't act to stop the transfer, four Republican committee chairmen from the House and Senate have written to the Obama administration asking them to reconsider.

"There is a broad range of important questions on both law and policy that remain outstanding with respect to the proposed transfer," Sens. John Thune, of South Dakota, and Charles Grassley, of Iowa, and Reps. Fred Upton, of Michigan, and Bob Goodlatte, of Virginia, wrote in a letter to U.S. Attorney General Loretta Lynch and Commerce Secretary Penny Pritzker.