var layer_group = new OpenLayers.Layer.WMS(
        "Sample Layer Group",
        "http://localhost:8081/geoserver/wms",
        {layers: "layer_group_name", transparent: true},
        {isBaseLayer: false, visibility: false}
    );
    map.addLayers([layer_group]);

map.events.register('click', map, function (e) {
        var url =  layer_group.getFullRequestString({
            REQUEST: "GetFeatureInfo",
            EXCEPTIONS: "application/vnd.ogc.se_xml",
            BBOX: layer_group.map.getExtent().toBBOX(),
            X: e.xy.x,
            Y: e.xy.y,
            INFO_FORMAT: 'text/html',
            QUERY_LAYERS: layer_group.params.LAYERS,
            WIDTH: layer_group.map.size.w,
            HEIGHT: layer_group.map.size.h});

        window.open(url,
                "getfeatureinfo",
                "location=0,status=0,scrollbars=1,width=600,height=150"
            );
    });

var layerlist = "layer1:inci,layer2:cableline"
var url =  layer_group.getFullRequestString({
        REQUEST: "GetFeatureInfo",
        EXCEPTIONS: "application/vnd.ogc.se_xml",
        BBOX: layer_group.map.getExtent().toBBOX(),
        X: e.xy.x,
        Y: e.xy.y,
        INFO_FORMAT: 'text/html',
        QUERY_LAYERS: layerlist,
        WIDTH: layer_group.map.size.w,
        HEIGHT: layer_group.map.size.h});