Ritzy Cinema workers in Brixton get paid a minimum of £8.80 an hour. Bectu is calling for an increase to £9.40 an hour.
Union bosses said Picturehouse Entertainment is being "very hard faced" and has refused to negotiate.
Picturehouse said pay would rise to £9.10 an hour on 2 September as part of a three-year agreement with Bectu.
Balloting began on Tuesday and will end on 30 August.
Two years ago staff held 13 strikes over their pay and the minimum wage was raised from £7.53 to £8.40 in January 2015 and then to £8.80 in September.
The London living wage has since gone up from £8.80 to £9.40 per hour.
Bectu said the company rejected offers to hold talks at the conciliation service Acas.
The union also wants Picturehouse to address issues about treatment of new staff, maternity and paternity leave, and night pay.
Bectu's assistant general secretary, Luke Crawley, said: "Bectu has tried to talk to Picturehouse but the company are being very hard faced in ignoring our pay claim.
"No one wants to go on strike and we would rather settle this by talking but the company has ignored our offer.
"Members need to vote yes and send a strong message to the company."
Staff at a cinema are being balloted by a union calling for the London living wage to be paid.