Dock your pay
Make a deduction from a person's pay.
Ships may be docked and these days so may spacecraft and even computers and phones. That meaning of docking is 'join together, by bringing into an anchorage or resting place'. The docking of pay is altogether different. That relates to the Old English 'dock' - 'to cut short, particularly of the hair or tail of an animal' and that practise is still commonplace in the dog and horse breeding communities. That form of the word dates back to at least the 14th century, when it was used by Geoffrey Chaucer in The Reeve's Tale, from The General Prologue of The Canterbury Tales, circa 1386:
His heer was by his erys ful round yshorn;
His top was dokked lyk a preest biforn
[His hair was cut round even with his ears;
His top was tonsured like a preacher's.]
This use of 'dock' has nothing to do with ships.
Docking was a generally used term meaning 'cut short' for many centuries before it began to be specifically associated with the withholding of payment. That usage dates from the late 18th century. An early example of it is found in the records of one of the founding fathers of the USA - The Writings of James Madison: 1783-1787:
They [Officers of the Eastern line] will not only be docked of their half-pay, but will run great hazard of being put off with regard to a great share of their other pay.