That very much depends on the country's laws - here in Prague, there are no fewer than seven different transport companies providing public transit. The traveller doesn't need to know or care that the bus line 292 is run by one company, line 165 by another, yet another runs 314, yet another runs the light rail and another runs the normal trains - the fare is integrated, so tickets are valid for all of these. The integrating organization (which IIRC holds auctions for licenses on each of the lines) is city-sponsored, so you could call that a government influence. It should be noted that this is a system that's been taking hold for some ten years now, and that the majority of public transit is still provided by the city's public transit company.