The answer is Business.
Labor unions do hire lobbyists to represent their interests, particularly in areas related to workers' rights, wages, and labor laws. However, they do not hire as many lobbyists as businesses.
Governments, including state and local governments, do employ lobbyists to advocate for their interests at the federal level. However, their lobbying efforts are not as extensive as those of businesses.
Trade associations, which represent specific industries or sectors, also hire lobbyists to influence legislation and regulations. While they are significant players in lobbying, they do not surpass businesses in terms of the number of lobbyists hired.
Businesses are the largest employers of lobbyists in Washington. They have significant resources and a vested interest in influencing legislation and regulations that affect their operations. This includes a wide range of industries, from technology to pharmaceuticals, which collectively hire a substantial number of lobbyists.