It's a domestic issue of those dissatisfied with the government. The protest was limited to the area around the Ministry of Finance (MoF). Apparently, the protesters are not happy with the current PM, probably because she's the sister of ousted former PM Thaksin. The leader of the protest is an ousted deputy PM. Overall, it does not involve any foreigners or tourists. The protesters agreed to leave the MoF but it seems Suthep (the ousted former PM) is encouraging the occupation of three more ministry buildings.
I was in BKK in the late-80's or early-90's when there was a major protest around the government buildings. I had no idea about it until I got back to the US and people asked me what was going on. Of course, online communication was nothing compared to what's available today.
For more current info, check the newspaper links below.
Thailand protests,Thaksin,constitution,politics,amnesty bill,Thailand News,Thai Coup,Thai News Online,Thai Newspaper,Nation News,News in Thailand,aec ,asean
Bangkok Post