UPDATE 1-AstraZeneca staff set 3 strike dates in September

* GMB union says strikes set for Sept 8, 15, 22

* Action centred at Macclesfield manufacturing site

* Workers protesting over plan to freeze pension scheme

* Astra doesn’t see a significant impact on drug supply

(Adds AstraZeneca comment, paragraph 6-7)

LONDON, Aug 24 (Reuters) - Union members at AstraZeneca AZN.L will take accelerating strike action on three days next month over a plan to freeze the pharmaceutical group's final salary pension scheme, the GMB union said on Tuesday.

The action will involve three two-hour strikes on Sept. 8, three four-hour strikes on Sept. 15 and a 24-hour strike starting at 0500 GMT on Sept. 22. Further action will be announced in due course, the GMB added in a statement.

“The last thing our members want to do is to take strike action at AstraZeneca but the attack by the company on the pension entitlement of our members leaves them with no choice,” said GMB National Officer Allan Black.

“The strike action follows a GMB ballot of its members in the company in the light of this highly profitable pharmaceutical company’s decision to make savage cuts in its employees’ defined benefit (sometimes called final salary) pension scheme.”

About 2,500 workers are affected by the changes, mainly based at Macclesfield in northern England, the company’s second largest site.

AstraZeneca said it was very disappointed by the GMB decision, based on only 165 of its 469 members in the workforce voting for a strike. AstraZeneca employs approximately 9,000 people in Britain.

A spokeswoman added the action was not expected to have a significant impact on the supply of medicines, since the company has robust business continuity plans.

Final salary pensions are becoming a rarity for British workers, as companies move to cheaper defined-contribution schemes that limit their future financial exposure. (Reporting by Ben Hirschler; Editing by Louise Heavens and Jon Loades-Carter)