ATHENS, June 25 (Reuters) - Greek betting monopoly OPAP got shareholder approval on Wednesday to amend part of its corporate charter as it prepares for a possible opening of the country's gaming market.

Europe's biggest betting firm will adopt tougher measures against gambling addiction, one of Greece's main arguments against the EU which has been mounting pressure on the country to lift gaming restrictions.

"The shareholders meeting approved the amendment of article 2 of the firm's charter to include in its mission the adoption of consistent and systematic measures as part of the state policy against gambling," OPAP said in a bourse filing.

The approved changes also allow OPAP to offer consulting services outside Greece.

OPAP, 34.4 percent owned by the state, currently offers sports betting and lotteries in Greece through 5,400 outlets and has exclusive rights to do so until 2020.

Last week, it revealed plans to restructure operations by the end of the year to become more effective and seek further growth at home and abroad.

© Brought to you by Reuters