"Tighter rules" refer to stricter or more rigid regulations or guidelines. It means that restrictions or requirements are being placed with more stringency or in a more comprehensive manner. Full definition
Travel costs for state lawmakers has increased even amid tighter rules for how that money is supposed to be spent. (nystateofpolitics.com)
Those are the places I would want to focus on, along with tighter rules on marketing to children and things like that. (thelunchtray.com)
Millions of homeowners wish they could refinance, but their lenders tell them they can't qualify for today's low rates because of tight rules. (npr.org)