Some countries have a register of lobbyists, some do not and some have talked about it. Some suggest it to be compulsory, some it is optional.
In the US people paid to lobby must register with the secretary of the Senate and the clerk of the House of Representatives within 45 days of contacting a legislator for the first time, or 45 days after being employed.
An exception is that lobbyists who earn less than $3,000 per client for each quarter, or whose total lobbying expenses are less than $11,500 each quarter, do not need to register.
Part-time lobbyists are exempt from registering unless they spend more than 20% of their working hours doing lobbying activities in any quarter. If lobbyists have two or more contacts with a legislator as a lobbyist, then they must register.
Requirements for registering also apply to companies that specialize in lobbying, or ones that have an in-house lobbyist, particularly if they spend more than $11,500 on lobbying.