Americans are big tippers. Every year, we leave more than $30 billion in tips, mostly in restaurants but also casinos, nail salons and other service businesses. Traditionally, the owners of those businesses have not had much control over how tips are distributed. But a proposed rule from the Trump administration could change that. “This rule has really been pushed by the restaurant industry,” said Heidi Shierholz, chief economist for the Labor Department during the Obama administration.