This legislation already exists. Predatory underpricing has been a known problem for century, and is already built into antitrust laws. The thing is that it's

This legislation already exists. Predatory underpricing has been a known problem for century, and is already built into antitrust laws. The thing is that it's not generally illegal in its own right - it just forms a component of a potential antitrust case case which could result in the breakup of a company in conjunction with other anti-competitive or monopolistic behaviour. But the precedent is there. A company destroying its competition by operating at a loss and surviving entirely by virtue of external capital injection surely falls at the very least under the spirit if not the letter of antitrust laws.