On Tuesday the Dutch energy conglomerate’s US offshoot confirmed that it will continue to represent the interests of domestic refiners during the next round of negotiations, which are scheduled to take place tomorrow.

“While we continue running our business, we look forward to reaching a mutually satisfactory agreement with the USW,” the company added.

The statement follows the release of a letter in which Aamir Farid, the vice president of Shell’s US manufacturing division, told staff his company was “disappointed” that the union “seems unwilling to achieve a timely and reasonable agreement”.

Farid also outlined the key components of a contingency plan that calls for the use of independent contractors to keep plants impacted by the strike running.

This revelation outraged the USW and its supporters since the executive's correspondence was released two-days before negotiations were set to resume.

The timing of the release and subsequent reaction is fuelling fears that the standoff may continue. If fences are not mended within the next few days some forecasters are concerned that more strikes will follow.

Union officials maintain the fight is over safety issues that are believed to be the underlying cause of more than two dozen deaths and hundreds of injuries.

Shell says it is "committed to safety" and claims the dispute stems from the rejection of proposals to replace routine maintenance contractors with USW affiliates.

In a recent briefing Michael Webber, an analyst at Wells Fargo Securities, reminded clients that nearly 7,000 employees from 15 different refineries are on strike. He also noted the first wave, which began on 1 February, only impacted nine plants.

“The strikes now include more than 6,500 workers at 15 refineries, up from 3,800 workers at nine refineries,” he wrote.

“Were US refineries forced to halt crude processing, we would expect a positive reaction for both crude and product tankers (via vessel dislocation, delays, and floating storage).”

Industry observers are quick to point out that the strike represents the largest refinery walkout the nation has seen in nearly 40 years.

Today’s tally includes refineries and chemical plants in Texas, Washington, California, Kentucky, Ohio, Indiana and Louisiana. Union labour with ties to facilities in other states have threatened to strike as well.