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."

The chief minister of Punjab province, Shahbaz Sharif, ordered a judicial inquiry into reports that hundreds of children had been abused over a period of several years.
Local media say a gang made videos showing the abuse of children, whose parents were then subject to blackmail.
The scandal centres on a village near the city of Kasur.
Reports say about 280 children, mostly under 14-years-old, were abused and filmed, in the village of Husain Khan Wala.
Correspondents say many victims are afraid to report abuse, in a society which allows abusers to brag about their exploits but stigmatises their victims.
Police say more arrests are expected.
Analysis by the BBC's Ilyas Khan in Islamabad
Child sex abuse is widespread in parts of Pakistan, especially in the countryside.
According to one estimate, over 3,500 cases of child molestation were reported in 2014, of which 67% were reported from rural areas.
Meanwhile, many have noticed that most of the clips being investigated date back to 2009-11, shortly after camera phones first became widely available, with few recent cases being reported.
This has led some to suspect that the clips were reported to the police amid a local dispute.
One boy told BBC Urdu the abuse began when he was 11, five years ago:
"They sexually abused me in front of secret cameras... they came back a week later and showed me the video, and said if I did not do what they wanted, they would show it to my friends and school colleagues."
A woman told the BBC her son had been molested and blackmailed for five years, and she had only recently learned about the abuse:
"They used to badly treat him wherever they could get hold of him. They would snatch his mobile and money.
"They [the perpetrators] are now threatening us."
District police officer Rai Babar Saeed told BBC Urdu: "We have around 30 video clips of one incident showing six victims and seven people involved. We have arrested these seven. We are still trying to recover more videos."
He added that there was "no political motive" behind the investigations, which he said were being conducted "on merit".
Last week, more than 20 people were injured as families of the alleged victims clashed with police in Kasur, accusing the authorities of ignoring their complaints.
Saba Sadiq, the head of Punjab's child protection bureau, described the case as "the largest child abuse scandal in Pakistan's history", the AFP news agency reports.
The provincial chief in Punjab is the brother of Pakistan's Prime Minister Nawaz Sharif.
Staff at a cinema are being balloted by a union calling for the London living wage to be paid.
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Seven people have been arrested in Pakistan on suspicion of involvement in child sexual abuse and extortion.