Treadmills will grind to a halt in south London tomorrow, as gym instructors hit back at privateer divide-and-rule tactics with a two-day strike.

Forty-eight recreation assistants, fitness coaches and swimming instructors employed by contractor Fusion Lifestyle will down whistles in protest at the company’s use of a “multi-tier workforce” in Croydon — where workers are paid at different rates for doing the same work, according to union Unite.

Workers will stage a 48-hour walkout from midnight tonight at five leisure centres in the Tory-controlled borough.

Meanwhile, Unite reps will treat council staff employed at the Bernard Weatherill House borough offices to a free breakfast and union “freebies.”

And Unite intends to stage a series of protests at Fusion’s leisure sites in Southwark to raise awareness of the company’s practices across its council contracts.

Unite regional officer Onay Kasab said: “We are disappointed that, despite committing to providing proposals to deal with our concerns about the multi-tier workforce, where staff doing the same job are on wildly varying pay and conditions, the employer has failed to even make contact with the union.

“We have made clear we are prepared to negotiate — the company clearly is not.

“More widely, the leisure industry pays some appallingly low wages, uses zero-hours contracts and now is leading the way in not passing on pay awards to contracted-out staff.

“Unite has committed to taking on the bosses in this industry and winning respect and dignity at work for our members.

“We call on Croydon Council to intervene and tell Fusion to start treating its workers with fairness, not contempt.”

Fusion did not respond to the Star’s calls asking for comment.

The union is taking on the extreme exploitation in the leisure industry — later this month it will ballot workers at self-declared social enterprise Greenwich Leisure, where two-thirds of workers are on zero-hours contracts.

Next month, the minimum wage will be raised to £6.31 an hour — which is above the lowest rates of pay in local government.