More than 4,000 workers including security guards, engineers and drivers will walk out on July 26 and 27, and August 5, 6, 23 and 24.
It comes after workers backed strike action in eight ballots.
Unite said the action follows the rejection of an 18-month pay offer amounting to £3.75 extra a day for the lowest paid.
It predicted the walkout “could potentially shut down the airport”.
The union claimed there is growing frustration over pay disparities between workers doing the same job, as well as the “massive” pay package earned by Heathrow chief executive John Holland-Kaye, whose basic remuneration rose from £2.1 million in 2017 to £4.2 million last year.
Unite regional coordinating officer Wayne King said: “There is deepening anger over pay among workers who are essential to the smooth running of Heathrow Airport.
“They are fed up of being expected to accept crumbs while the chief executive pockets an eye popping 103% rise in his pay package and shareholders are handed dividends of over £2 billion in the last two years alone.
“To add insult to injury there are widening pay disparities leading to airport security guards employed after 2014 earning up to £6,000 less than colleagues hired before that date.”
He added: “Bosses at Heathrow Airport need to get their heads out of the sand and start negotiating meaningfully over pay.
“Otherwise there will be significant disruption to flights to and from Heathrow and the potential closure of the airport over the summer months because of industrial action.”
A Heathrow spokesman said bosses remain committed to finding a solution: “We are disappointed that Unite will be taking strike action.
"Following this decision, we will be implementing contingency plans that will ensure the airport remains open and operating safely throughout any coordinated action.
“We will be working alongside our airline partners to minimise disruption caused to passengers as they look towards their well deserved summer holidays.
“We have proposed a progressive pay package giving at least a 4.6% pay rise to over 70% of our frontline colleagues.
“The total package offered is above RPI and is specifically designed to boost the wages of lower paid colleagues.
“We have invited our union colleagues back to the table and urge them to continue working with us to reach an agreement.”