Corker said it makes "very little sense" to continue to require this corporate welfare to companies, and said his amendment to the 21st Century Postal Service act, S. 1789, would eliminate current law that limits the ability of the USPS to raise the price of some services.

That change is just one of many that Corker is proposing in his amendment. Other language in his amendment would allow the USPS to continue with its own recommendations to close post offices around the country, and move to five-day delivery right away. Corker criticized S. 1789 for calling for a two-year study on stopping Saturday delivery.

"We don't need a study to tell us what we already know," he said. "The post office needs flexibility in its delivery schedule."

His language would also eliminate the "no layoff" clause for postal workers in future contracts, and kill language mandating that the fringe benefits of postal workers meet the standards of benefits in 1971.

Like other Republicans, Corker took a tough line on the need to make these sorts of changes, and said they would help stop the fiscal hemorrhaging of the last few years. Corker said the USPS lost $5.1 billion in the last fiscal year, and $3.3 billion in the first fiscal year of 2012.

Democrats have said these losses are due to a requirement that the USPS pre-fund its retirement health benefits, but Corker rejected that.

"The fact is, these recent losses are not, and let me underline, not due to the pre-funding requirement, because Congress has allowed the USPS to delay this last year's payment," he said.

"The U.S. Postal Service is absolutely not sustainable in its current form," he added. "Mail volume has greatly declined over the last decade and will continue to decline over the next decade.

"The United States Post Office has known this for a long time, they knew that mail volume was declining, and that the market for their product was changing."

The Senate will consider as many as 39 amendments to the bill on Tuesday, and Corker's and other GOP proposals are unlikely to survive, since each will need to win 60-votes for passage. Sen. Susan CollinsSusan Margaret CollinsOvernight Tech: Judge blocks AT&T request for DOJ communications | Facebook VP apologizes for tweets about Mueller probe | Tech wants Treasury to fight EU tax proposal Overnight Regulation: Trump to take steps to ban bump stocks | Trump eases rules on insurance sold outside of ObamaCare | FCC to officially rescind net neutrality Thursday | Obama EPA chief: Reg rollback won't stand FCC to officially rescind net neutrality rules on Thursday MORE (R-Maine), who co-sponsored S. 1789, said she would oppose Corker's language, and said Congress should give the USPS more time to find ways to cut costs, and should not mandate cuts right away.

"I believe that cutting Saturday delivery should be the last resort, not the first option, because it will inevitably drive away customers," Collins said. "But again, we have said that if there are no other alternatives this measure could proceed, but I can't imagine any large business operating this way — cutting service first."