According to a news story on thaivisa.com, which translates an Immigration announcement from Thai to English, Non-Immigrant Visa or Tourist visa holders with time remaining on their visa can exit and enter Thailand as before.
These new measures are targeting instead foreigners who arrive in Thailand without a visa, and who then regularly enter and exit the kingdom every 15 or 30 days as a way of extending their stay in Thailand.
The report says that from yesterday (May 10) visitors may enter into Thailand via a land border only once. After that they will be refused entry to the Kingdom and - if they wish to re-ennter the country, must fly out and return with a visa obtained from a Royal Thai Consulate in a neighbouring country or elsewhere.
The Immigration Bureau has confirmed that further restrictions are to be enforced from August 12.
The report concludes by saying that a number of Thaivisa members have confirmed that these restrictions are being enforced at the Mae Sai border crossing in Chiang Rai province, with some members saying they are stranded at the border unable to enter Thailand.