The threat of a strike at the Port of Charleston this weekend has been averted.

The International Longshormen’s Association and shipping companies have agreed on a tentative deal on one key issue and on an extension until Feb. 6 to iron out the remaining details, officials announced Friday.

Federal mediators have been trying to push contract negotiations along between the ILA and shipping companies after talks broke down this month, and a potential strike could have started as early as Sunday.

Federal Mediation and Conciliation Service director George H. Cohen organized a last-ditch meeting days ago to try to bring both sides to a resolution. In a statement Friday, he announced the extension and progress on a major sticking point, royalty payments to ILA members.

“The container royalty payment issue has been agreed upon in principle by the parties, subject to achieving an overall collective bargaining agreement,” according to the statement.

The sides have until midnight Feb. 6 to come to terms.

The extension stops 14,500 members of the ILA from going on strike Sunday, a stoppage that would have closed several ports along the East Coast, including Charleston’s.

Ken Riley, president of ILA Local 1422 in Charleston, could not be reached for comment Friday.

The last major ILA work stoppage was in 1977.

The master contract between the ILA and the U.S. Maritime Alliance, a group representing shipping lines, terminal operators and port associations, expired in September.

The two sides agreed to extend the contract once already, for 90 days, and were initially reluctant to go beyond Sunday.

The union has said its members would agree to an extension only if the alliance drops a proposal to freeze the royalty payments workers get for every container they unload. The alliance has argued that the longshoremen, who it said make an average $124,138 per year in wages and benefits, are compensated well enough already.

The threat of a strike prompted contingency plans among some manufacturers in South Carolina in recent days. The State Ports Authority extended operation hours in recent days at its busiest container terminals to move cargo.

SPA spokeswoman Allison Skipper said SPA terminals would stay open two extra hours Friday and return to regular operations today.

The added flow at Charleston ports already has meant more trips for several trucking companies, including Superior Transportation in North Charleston.

On Friday morning, a convoy of 12 company rigs descended on the SPA’s Columbus Street Terminal on the Charleston peninsula to pick up large auto supplies initially planned for pickup next month, according to owner Pat Barber.

Barber said the earlier pickup meant the 36-truck company would be without the dozen rigs for more days than initially planned.

“They’re loading up on a project that doesn’t start until January, but we wanted to get it out of there just in case,” he said.

Reach Tyrone Richardson at 937-5550. The Associated Press contributed to this story.