where can i find the rules regarding at what dollar figure of payment
to casual labor employees per annum is it required that the employer
must withold taxes from payments , and include record of that
employment on quarterly or annual tax reports.

For Federal Income Taxes, get both of the following two documents.

1. Circular E, Employer's Tax Guide, contains most or all of what you
want to know:
  http://www.irs.gov/pub/irs-pdf/p15.pdf

2. Workers will be getting more money in their paychecks thanks to the
Jobs and Growth Tax Relief Reconciliation Act of 2003. New withholding
tables incorporate the lower tax rates for employers to use when
figuring the federal income tax to withhold from their employees’
wages:
  http://www.irs.gov/pub/irs-pdf/n1036.pdf

If the state in which the employees work withholds money for state or
local income taxes, you'll need similar information from that state.

It depends on which country you are talking about.