Warsaw — Poland's Jozef Cardinal Glemp issued a warning against unofficial May Day rallies, a pro-government Roman Catholic daily said. Cardinal Glemp said unofficial rallies could lead to trouble, the daily reported. It was the first authoritative comment by the church on an appeal by the Solidarity underground for people to boycott traditional Communist marches and to turn out for mass rallies. The leader of the former trade union movement, Lech Walesa, has tacitly endorsed the underground's appeal. He returned to work at the Lenin Shipyards as an electrician. His base salary: about $300 a month.