Hull City Council and Humberside Police wrote to the developers of the Lord Line building claiming poor security was putting lives at risk.
The council said it was now issuing a legal enforcement notice against owners Manor Property Group.
The firm said it was in talks with the authority.
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The former trawler company offices at the old St Andrews fishing dock in Hull have stood empty for a number of years and have featured on urban explorer websites.
Police said they had been called to the building a number of times and were concerned somebody might be killed while exploring the two-storey structure.
Manor Property Group, which is planning to redevelop the site into a "maritime educational campus", claimed the building had now been made secure.
In a statement, the company said: "As yet we do not have a complete solution, accordingly the detail remains private."
Action is being taken to force the owners of a derelict building to make it safe amid police fears trespassers could be killed.