A last-ditch attempt is being made by US ports employers group United States Maritime Alliance (USMX) to avert a port workers strike that threatens to shut down the country’s ports at midnight EST on Monday.

USMX has submitted a new offer to the International Longshoremen’s Association that it claims would increase wages by nearly 50%, triple employer contributions to employee retirement plans, strengthen health care options and “retain the current language around automation and semi-automation”.

“In the last 24 hours, the USMX and ILA have traded counter-offers related to wages. The USMX increased our offer and has also requested an extension of the current Master Contract, now that both sides have moved off their previous positions. We are hopeful that this could allow us to fully resume collective bargaining around the other outstanding issues — in an effort to reach an agreement,” USMX said in a statement released late on Monday evening local time.

The ILA has yet to respond to USMX’s statement.

The labour contract between the ILA and USMX is set to expire in just hours, which covers container and vehicle terminals on the US East Coast and Gulf Coast.

A resulting strike could cost the US economy between $300m and $5bn per day, according to analysts.