The Professional Footballers' Association says it will resist moves to introduce drug testing for players away from the training ground.
Gordon Taylor believes testing at home is an invasion of privacy
The measures would mean testing players at home - and on their days off.
But PFA chief executive Gordon Taylor told the News of the World: "It is a total invasion of their privacy.
"The players will fight this and this could be a test of strength. It's too early to talk of a strike but we will take a tough stance over this issue."
Uefa has already introduced the measures, meaning players involved in the Champions League can have visits from drug testers at their homes.
The World Anti-Doping Agency is keen to see football adopt its strict drugs code, which demands athletes can be tested at any time.
However, Taylor added: "Players feel they have little privacy as it is but these measures would make them feel they have none at all.
"We already have an agreement with the Football Association to have mandatory testing after matches and at their training grounds.
"Football is a team game and not an individual one like athletics, which is why the current testing is adequate."
But Wada chairman Dick Pound said: "By testing players only at training it gives them the chance to get away with drug use."