The firm said difficult trading conditions in the shellfish market, particularly in the export sector, had left it with no option but to close the site, formerly the Sco-Fro plant, and transfer operations to its main langoustine processing facility at Buckie in Moray.
The 27 Lochaber employees have been offered alternative employment within ASL, although the company said at this stage there is "no indication" how many staff may take this option.
ASL took over the plant on the Annat Point Industrial Estate from Sco-Fro last year. The company supplies whole Scottish langoustine to a wide range of export markets, including Europe and the Middle East.
The closure, scheduled for Friday, comes amid critical times for the west coast shellfish industry.
The main European importers, particularly Spain and Greece, have been mired in the Euro crisis, while record fuel costs and low produce prices have forced a number of suppliers and independent fishermen to close in the past year.
In a statement released on Tuesday, a spokesman for ASL said: "We regret having to take this decision and we are very sorry for the impact this will have on employees.
"However, after undertaking a full review of the site, it was decided that the only viable option for the business was to close the facility.
"We have offered alternative employment within the ASL group for everyone affected, but we do appreciate that for many people this will not be an option because of their close ties to the Fort William area."
