The action would be the first of a series of walkouts planned for this month.
The dispute has been provoked by bosses’ new cuts plan.
The union said 200 jobs and “the safety regime that ensures a guard on every train” are under threat.
Bosses want train guards and other onboard staff roles to be combined, leading to higher workloads and undermining safety.
The RMT said the rail franchise run by Virgin and Stagecoach was showing a “cavalier attitude to safety”.
It said bosses had mobilised a “scab army of managers” to undermine workers’ action.
The dispute is one of a series across the rail network that have seen strikes in recent months.
Two further 24-hour strikes are set for Friday 26 and Monday 29 August with an overtime ban in between.
Virgin took over East Coast Mainline last year, after it had been successfully run under public ownership since 2009.
Rail unions, passengers and campaigners rightly fought against the selloff.