* Strike could begin as early as Wednesday
* Contract talks continuing through weekend
(Adds details, background, byline)
By Erwin Seba
HOUSTON, Jan 28 (Reuters) - The United Steelworkers union warned on Saturday that a strike by U.S. refinery workers as early as 12 a.m. Wednesday was becoming more likely due to "the lack of a more substantive response from the industry."
Union and oil company negotiators have been meeting since Jan. 17 to hammer out a new three-year agreement for workers at nearly two-thirds of U.S. refining capacity.
Union negotiators have not sent out a similar warning to refinery workers in the past three rounds of contract talks with the industry.
A representative for Shell Oil Co, the U.S. unit of Royal Dutch Shell Plc, which is the lead oil company negotiator, was not immediately available to discuss the union statement.
As late as Friday, Shell said it was optimistic an agreement could be reached with the union.
In the statement issued Saturday night, the USW's bargaining committee said that without further progress in the talks a strike could take place at "one or more locations when the collective bargaining agreements expire."
Talks between the two sides were scheduled to continue through the weekend.
USW spokeswoman Lynne Hancock said the union would make no further statements on Saturday.
In the lead-up to this year's talks, the Steelworkers union warned that the lack of improved safety protections for workers at the nation's refineries could bring about the first nationwide strike since 1980.
Eighteen workers have died at U.S. refineries since the last agreement in 2009, according to the union.
As much as 11 percent of U.S. refining capacity could temporarily shut due to a strike lasting three months, sources have said.
In addition to possible shutdowns, oil companies have been training temporary replacement workers to continue to operate their refineries in the event of work stoppage.
One source said refiners' preparations for a possible strike are unlike any seen in 20 years.
Industry analysts have said they thought the chances of a strike were slim.
During the 1980 strike, refiners kept their plants in operation by using trained supervisors and engineers to replace hourly workers who operate and maintain equipment. (Editing by Chistopher Wilson)