Pfizer employees have walked off the job at the company’s Perth manufacturing plant as they push for an improvement to a ‘‘substandard’’ wage offer.

The pharmaceutical giant has offered its Perth-based employees a five per cent pay rise this year, followed by four per cent and three per cent increases over the following two years.

Workers represented by the United Workers Union are seeking a combined 18 per cent increase over the same period, pointing to the drug-maker’s $US22 billion ($32 billion) profit last year.

The two parties are also at odds over redundancy payments as Pfizer prepares to shutter the Bentley plant in 2024.

Workers on Tuesday began a 24-hour period of industrial action, with the union warning members reserved the right to take ‘‘indefinite action’’ unless Pfizer improved its offer.

‘‘Pfizer’s revenues have doubled in two years, largely on the back of the world’s taxpayers who forked out to have the COVID-19 vaccine distributed in their respective countries,’’ the union’s allied co-ordinator Louise Dillon said.

‘‘Australians contributed hundreds of millions of dollars to Pfizer’s profit margins but the company is insistent on squeezing every single dollar, even if it means screwing workers out of a fair pay deal.’’

Pfizer said it had delivered above-inflation pay increases across the past decade.

‘‘Pfizer is working closely with the union to agree on an (enterprise bargaining agreement) that works for all employees, which offers fair and reasonable terms for wages and allowances, and addresses the increased cost of living,’’ a spokesperson said.

‘‘The latest pay increases are also in addition to an approximately 10 per cent bonus payment delivered in April this year, and a COVID-19 bonus payment last year.’’

The company rejected a union claim that workers could be short-changed when the facility closed, saying uncapped redundancy provisions remained intact and exceeded those provided under national employment standards.

Products manufactured in Perth will be made at the company’s Melbourne site once the Bentley plant closes.