A toilet paper maker wants hundreds of thousands of dollars in damages from its own workers and their union following strike action it says was unlawful.

Asaleo Care New Zealand lodged papers in Employment Relations Authority against the Pulp and Paper Workers Union and more than 60 individuals who work at the Kawerau Mill making brands such as Purex.

Lawyer John France argues that a strike held on July 27 this year had been notified to start at 12.15pm that day, but instead began an hour earlier at 11.15am.

"Therefore, the strike is unlawful because it commenced before the date and time specified in the strike notice."

He told the authority that the strike and breach of contract had caused financial loss of at least $542,852.

Asaleo was now seeking "penalties from each and every second respondent ... arising out of the...breaches of their terms and conditions of employment".

The Pulp and Paper Union is the first respondent.

Secretary Tane Phillips said the union would be defending the lodging "vigorously".

"It's all about their own vindictiveness, trying to get these guys to kowtow to bend the knee to sign their so called good agreement."

Industrial relations were already bad, with staff having been locked out of the mill since the beginning of the month, meaning 145 members have been prevented from going to work and getting paid.

The lockout was imposed by the company after wage negotiations broke down over the union’s claim for a pay rise equal to the rate of inflation.