US Libertarians think all borders should be open. People should not be restricted from moving from place to place. The main debate in US around this issue is of course between liberals and conservatives. Liberals like immigration because they are pro wealth redistribution, poor people who come to US vote for them because they will get free hand outs. Conservatives are against immigration for two reasons, on one hand they will lose political power if minorities start to grow in numbers, and for two they will be forced to fund social programs that support the newly immigrated minorities. Libertarians are against force being used to fund social programs, so they are okay with anybody moving anywhere, but they are against anybody being supported by social programs that are funded with force. So for libertarians it is really not an issue, the primary reason immigration is such an issue for conservatives and liberals is because of government funded social programs. Libertarian also have nothing against labor unions. Everything is contractual, there is nothing wrong with a group of workers voluntarily contracting together to form a labor union.