UPDATE 1-Indonesia's Telkomsel workers plan to strike to end-Dec

(Adds details, quotes)

JAKARTA Nov 9 (Reuters) - Workers at Indonesia's Telkomsel, the mobile phone unit of the country's biggest telecoms firm Telekomunikasi Indonesia , plan to strike over pay from Thursday until the end of December, their union said on Wednesday.

The union's chairman Achsinanto Risantosa told Reuters that the strike, the latest in a series of industrial disputes in Southeast Asia's biggest economy, could hurt the operations of Telkomsel, part owned by Singapore Telecommunications .

"I am afraid that this will impact the operation of Telkomsel, and given that 68 percent of Telkom's revenue comes from Telkomsel, I am afraid it would impact Telkom's share price," he said.

Telkom's shares ended flat on Wednesday after news of the strike plan, versus a broader Jakarta index up 1.4 percent.

Telkomsel's president director, Sarwoto Atmosutarno, said he guaranteed that Telkomsel's service would not be disrupted due to the planned strike. He also said that management was opening room for dialogue with the union.

"We are examining this action because their demand is remuneration," he told Reuters.

"Telkomsel workers are paid much higher than the average pay of similar industries and are very prosperous because they are paid 24 months salary in a year," he added.

Risantosa said the strike was launched after repeated negotiations over pay and pensions failed to reach a deal, and that it will take place across Indonesia involving about 2,500 workers from a total of over 4,000 at Telkomsel.

The strike follows industrial action by supermarket employees at Carrefour , pilots at flag carrier Garuda Indonesia and miners at Freeport McMoRan Copper & Gold's giant Grasberg mine, as workers seek a greater share of profits in an economy growing at over six percent. (Reporting by Olivia Rondonuwu and Janeman Latul; Editing by Neil Chatterjee)