The "cash for clunkers" program will have to be suspended next week unless the Senate acts to authorize a $2 billion extension for the program, Transportation Sec. Ray LaHood said Sunday.

"If we don't get the $2 billion from the Senate...we would have to suspend the program next week," LaHood said during an appearance on C-SPAN's "Newsmakers" program.

LaHood said he expected the additional money for the rebate program would fund trade-ins of old autos for more fuel efficient vehicles through Labor Day.

"We believe the $2 billion we're very hopeful the Senate will pass this week...will take us through the time that Congress gets back after Labor Day," the former Illinois Republican congressman asserted.

Extended funding for the program passed the House this week by a strong, bipartisan margin, but may face more obstacles in the Senate. Sen. John McCainJohn McCainMcCain to support waiver for Mattis, Trump team says Senators crafting bill to limit deportations under Trump Trump picks Mattis for Defense secretary: report MORE (R-Ariz.) has signaled he may filibuster the bill, and a key Rust Belt Democrat, Sen. Claire McCaskillClaire McCaskillDefense bill tackles retaliation against military sex assault victims Red-state Dems face tough votes on Trump picks Vulnerable Dems ready to work with Trump MORE (Mo.) has already said she's disinclined to support the bill.

Furthermore, Sens. Dianne FeinsteinDianne FeinsteinOvernight Defense: Armed Services chairman's hopes for Trump | Senators seek to change Saudi 9/11 bill | Palin reportedly considered for VA chief Lawmakers praise defense bill's National Guard bonus fix CIA head warns Trump: Undermining Iran deal would be 'disastrous' MORE (D-Calif.) and Susan CollinsSusan CollinsSenators crafting bill to limit deportations under Trump Cornyn: ‘Virtual certainty’ Sessions and Price will be confirmed Trump's wrong to pick Bannon or Sessions for anything MORE (R-Maine), two of the authors of the initial "cash for clunkers" legislation, asked LaHood for more data on the cost and extent of the environmental impact of the program before the Senate reauthorizes the program.

"If the Senate does not pass the additional $2 billion, the program will get suspended," LaHood cautioned, while also asserting that the environmental standards contained in the first program should be left alone.

The Transportation secretary said that additional purchases using the vouchers will be continued throughout the week until the Senate acts.

If the Senate doesn't act in time, LaHood said the Obama administration would evaluate other options to extend the program.

"I think the conclusion is that the TARP money cannot be used for this," he said, adding that the administration has been evaluating redirecting other federal spending to support the program.

LaHood also defended the effectiveness of the program as one of the most stimulative bits of government spending embarked upon by the White House and Congress.

"It is probably the one real stimulus part that has worked very, very well," he said.