Talks between British Airways and unions have broken down, raising the odds of more strike action over the summer.
An unofficial strike by 250 BA ground staff over the weekend forced the airline to cancel hundreds of flights from Heathrow, the world's busiest international hub, disrupting the plans of more than 100,000 travellers.
BA executives and union officials have been unable to resolve the dispute in the last two days, and a spokesman for the GMB union has said the union would now ballot its members for industrial action.
BA, Europe's biggest airline, has said in a statement it offered to postpone the introduction of ATR until the two sides had negotiated the 2003 pay deal, but this was rejected.
As a result, it said it would introduce ATR at midday on Wednesday so that staff could see for themselves that there was no threat from the new system, a swipe card method for employees to clock in and out.
The unions and BA said they were willing to reopen talks to discuss the dispute.
BA Chief Executive Rod Eddington warned on Tuesday that the failure of modernisation plans threatened the airline's future. He said that the impact from the weekend's strike action would cost the company tens of millions of pounds.
BA has cut more than 10,000 jobs both to cope with the severe downturn in demand for long-distance air travel, and to compete with the booming European no-frills airlines.