With hours to go before their labor contract expired, longshoremen on the East and Gulf Coasts prepared on Monday to go on strike at midnight, halting most activity at some of the busiest U.S. ports.

But for the first time in months, there were signs of movement in negotiations. The employers’ group, the United States Maritime Alliance, said on Monday evening that it had “traded counteroffers related to wages” with the International Longshoremen’s Association and that it had asked to extend the contract expiring at midnight.

“Both sides have moved off their previous positions,” the Maritime Alliance said in a news release. “We are hopeful that this could allow us to fully resume collective bargaining.”

A spokesman for the I.L.A. did not immediately respond to a request for comment. Earlier Monday, Jim McNamara, a union spokesman, said in a statement that the Maritime Alliance had refused demands “for a fair and decent contract.”

The I.L.A., which has 47,000 members, has not held a strike at all the East and Gulf Coast ports since 1977. A walkout would cost the economy billions of dollars a day.

President Biden could use a federal labor law to force the longshoremen back to work, but on Sunday he said he was not considering using that power. In recent days, top government officials have pressed both sides to reach a deal.

Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.

Thank you for your patience while we verify access.

Already a subscriber? Log in.

Want all of The Times? Subscribe.