French union the CGT Wednesday called for open-ended strikes beginning Oct. 12 in the energy sector against the government's pension reform.

"This notification of a strike aims to allow employees to strengthen the balance of power in their favor following the broad strike action Oct. 12," the CGT's mining and energy arm said.

Unions have already carried out two one-day strikes in September. The last one--Sept. 23--was accompanied by rallies that brought 3 million people out into the street, according to unions.

France's six leading unions last week said they are planning a fresh one-day strike Oct. 12 and carried out a day of protest Saturday that they say again brought out 3 million people.

Open-ended strikes would step up the pressure on Nicolas Sarkozy's government, which has thus far pointedly refused to back down on the key aspect of the reform which would raise the retirement age to 62 from 60 by 2018.

The division of the CGT union for Paris' transport network the RATP Thursday also announced a notification of open-ended strike from Oct. 12.

-By William Horobin, Dow Jones Newswires; +33 1 4017 1740; william.horobin@dowjones.com