Amid the massive oil cleanup in the Gulf of Mexico, the domestic shipping industry is going on the offensive, cautioning Members not to tinker with an obscure maritime law it claims protects thousands of well-paying American jobs.

A repeal of the Jones Act “would put tens of thousands of U.S. mariners out of work,” said Mike Roberts, a senior vice president at Crowley Maritime Corp. “It would degrade our maritime border security in the Gulf region, when you replace tens of thousands of mariners with foreigners on foreign vessels. And it’s a key energy resource to the United States.”

Roberts added that a significant amount of petroleum comes out of the Gulf, “and American control over the vessels and the workers in that region is important from a security perspective.”

Roberts’ company is one of hundreds of transportation firms and unions working through the Maritime Cabotage Task Force to push back against what they claim is misinformation about the Jones Act, a 90-year-old maritime law that “mandates the use of American vessels and American workers in U.S. domestic maritime trade,” according to the group.

In recent weeks, an informal drive to repeal the Jones Act has echoed on cable television news programs, primarily by conservative pundits on Fox News and elsewhere to bash President Barack Obama’s handling of the oil spill.

On Fox in late June, conservative critic Tucker Carlson told Sean Hannity that the Obama administration was dragging its feet on the Jones Act to appease a major benefactor to his political party: organized labor.

“I think you know as well as I do, Sean, that it’s important to protect American union jobs,” Carlson said, according to a transcript. “I mean, these are faithful Democratic voters. Anything that might alienate the American labor movement is bad.”

Sen. John McCain (R-Ariz.), who is facing a tough primary battle this summer against ex-Rep. J.D. Hayworth, also has taken up the cause of repealing the Jones Act, sponsoring the Open America’s Waters Act on June 23.

“This antiquated and protectionist law has been predominantly featured in the news as of late due to the Gulf Coast oil spill,” McCain said in a statement after introducing the bill. “Within a week of the explosion, 13 countries, including several European nations, offered assistance from vessels and crews with experience in removing oil spill debris, and as of June 21st, the State Department has acknowledged that overall ‘it has had 21 aid offers from 17 countries.’ However, due to the Jones Act, these vessels are not permitted in U.S. waters.”

But the domestic shipping industry argues that the Jones Act doesn’t apply to foreign vessels assisting in the cleanup more than 40 miles out to sea.

Eric Smith, a vice president at Overseas Shipholding Group Inc., said in an interview that “there are plenty of vessels available to assist in the cleanup of the spill in the Gulf of Mexico.”

He also suggested that foreign shipping companies looking to get in on the lucrative task of cleaning up the BP spill may be behind the repeal efforts.

“Every piece of equipment being used in the cleanup comes with a price tag and there’s nobody out there who is doing this out of the goodness of their heart,” Smith said. “It all comes with the price tag, and I assure you it is not what normally would be the price for a lot of the offered equipment.”

“You can’t help but say there are folks who are clearly trying to take this as an opportunity in these difficult economic times,” he added. “And they’re leveraging everything possible out there to achieve a profitable margin.”

If the law is repealed, Mark Ruge, a lawyer for the Maritime Cabotage Task Force, estimates that $100.3 billion in economic output and 500,000 jobs may be at stake — workers who may have already had to switch gears following the April 20 explosion on the Deepwater Horizon rig that caused the spill.

“One of the ironies in the Gulf is that people who want to waive the Jones Act are essentially proposing to replace American jobs with foreign jobs,” Ruge said. “Many of the people who are working on the skimming ships are the very people who have had their futures destroyed by the oil spill, including fishermen and offshore supply vessel operators.”