With time running out before the current authorization of federal railroad programs expires at the end of September, it looks increasingly likely that lawmakers will postpone new rail legislation until next year and roll it into a bigger surface transportation bill.

Rail bills have yet to be introduced in either chamber — leaving insufficient time for lawmakers to take up the complex legislation in the brief window for congressional action in September. While the future of Amtrak has dominated early discussions about a rail bill, a fight between freight railroads and shippers who rely on the carriers is shaping up as a bigger stumbling block to a rail bill.

“Things are not looking good for this getting wrapped up by the end of the year,” said a lobbyist for commodities shippers who depend on freight railroads to move goods to market. “There’s just too wide a divide at this point.”

Rail operators represented by such groups as the Association of American Railroads have been waging a high-profile advertising campaign in recent months touting the billions of dollars of private sector infrastructure investment in freight railroads. House Transportation and Infrastructure Chairman Bill Shuster, R-Pa., is widely viewed as an ally of the railroads and has said he is aiming to produce a timely bill.

Businesses that move goods by rail or depend on railroads to carry raw materials — such as power plants that burn coal — are appealing to Senate Commerce, Science and Transportation Chairman Jay Rockefeller, D-W.Va., to help them challenge what they view as unfair increases in rail cargo rates in recent years.

“Lack of competition in the freight rail industry is hurting American manufacturers and producers,” a coalition of businesses that ship by rail said last week in a letter to Rockefeller. “The nation needs a pro-competitive national freight rail transportation system to ensure fair prices and reasonable service for rail-dependent shippers.”

Democrats from West Virginia — the nation’s second-biggest coal-producing state, which is reliant on railroads to move the product — have a long history of battling the railroads. West Virginia Democrat Harley Staggers was the House champion of a 1980 law (PL 96-448) that largely deregulated the rail shipping industry.

A 2007 report by the Government Accountability Office said freight rail charges for most goods had dropped considerably since changes mandated under the law took effect in the mid-1980s.

But the coalition of railroad users said in its letter to Rockefeller that railroad mergers have reversed that trend since the turn of the millennium, causing rates charged by railroads to increase 2.5 times faster than both trucking rates and the inflation rate since 2003.

Rockefeller faced intense opposition from the rail lobby in an ultimately unsuccessful attempt in 2009 to overhaul the Surface Transportation Board, which regulates the rail industry.

“I’ve been at this for years, and the railroads are still dead-set against any changes,” Rockefeller said. “They’re more powerful than the [Nation Rifle Association].”

Lobbyists representing a variety of rail operators and shippers say they expect the House will move first to produce legislation. With only nine legislative days scheduled for the House in September and other legislative priorities filling the calendar, it would be next to impossible to move a rail bill before the current authorization (PL 110-432) expires.

Additionally, Shuster’s committee is under pressure to produce a companion to Senate-passed water resources legislation (S 601).

Given the complexities of the bill and the likelihood that Shuster and Rockefeller will be at odds over freight rail cargo charges, the most likely scenario will be an extension this fall that pushes off the issue until next year.

John D. Boyd contributed to this report.