I have for the last several years visited USA as a visiting professor for aprox 1 month per year. Until now, I have been exempts from all US taxes and pay tax in the UK on my American earnings. This year I have been told that because this is the 3rd year I have visited on a J1 visa that I am no longer eligible for exemption in US. I only work in US for 4-6 weeks per year. The remainder of the year I live and work in UK. Is my employer correct?