It is quite common knowledge now that as from 2 weeks ago the Thai Immigration Bureau have had a major crackdown on tourists and residents crossing land borders.
The reasons are clear it is to tighten their borders and stop foreigners living in Thailand without a proper long stay visa and in their words some are working in Thailand illegally and using the border crossings as an easy way to stay under the radar and live a life in Thailand. This rule is not new it has been around for some time it is now being enforced more strongly.
The crackdown rule is fairly simple to understand for example if you enter Thailand on a 30 day visa on arrival you are permitted to cross a land border and then re enter Thailand on two occasions making your total stay 90 days, if you have made more than two back to back border land crossings you are probably going to be turned away.
If you have been in Thailand for a long time using different methods to stay in the Kingdom including long extensions or getting a number of tourist visa 60 days from Thai consulates surrounding Thailand you will probably also be turned away as the officer makes his decision on the amount of time and visas you have in your passport.
If you are staying in Thailand on a Non Immigrant visa multiple entry meaning you cross the border every 90 days or if you have a 2 entry or 3 entry tourist visa from your home Country then this new rule does not affect you it only affects Foreigners who do not have a visa in their passport.
If you are coming in and out of the airport e.g. you work offshore and you are a frequent traveler through the airport then you should not be affected.
OK what can you do? If you are planning to come to Thailand for a stay longer than 60 days then obtain a visa from a Thai Consulate in your home Country before you arrive most will allow you to do by the post.
If you need to go to the border on the 2 permitted land crossings then take with you your return ticket so you can show the officer your expected departure date and also something which shows were you are staying in Thailand.
These enforced rules are there to stop foreigners border hopping and forces residents to obtain a more permanent visa to live in Thailand which really should be the case anyway.
In layman terms 90 days including your free 30 day visa is permitted, but try and get a visa from a Thai Consulate before coming to Thailand your life will be so much easier.