The school bus drivers union will rally Saturday outside Veolia Corp. in Dorchester in an effort to persuade the company to reinstate two leaders who were fired for their roles in a strike last month, the union said. Nearly one month after the one-day strike, union vice president Steve Gillis and Stevan Kirschbaum, chairman of the grievance committee, were terminated by Veolia. Kirshbaum said at a press conference Friday that the company violated their contract by failing to provide fair benefits for the drivers and removing time clocks from the workplace. Two other union members have also been fired.Haven Orecchio-Egresitz can be reached at Haven.email@example.com. Follow her on Twitter @HavenTaylor.