More than 100 military officers are in this risk group.
Earlier Prime Minister Prayut Chan-o-cha had ordered the closing of construction sites for one month to contain the spread of Covid-19.
Restrictions have been imposed on workers' camps and construction sites in the Bangkok area, including controlling the movement of people in the four southern border provinces (Songkhla Province, Yala Province, Pattani Province and Narathiwat Province) by not allowing labour movement in all cases.
The Centre for Covid-19 Situation Administration had issued control measures on construction workers in Bangkok and surrounding areas, and soldiers had been dispatched to oversee these areas since early June.