The lower house of parliament on Wednesday approved legislation that would allow gas station stores to remain open 24 hours a day on major highways and routes heavily used by travellers.

The approval follows earlier backing of the changes by the senate, which also approved a motion in favour of Sunday shopping and for longer minimum hours during weekdays and Saturdays.

But left-wing parties and unions are already planning to challenge any such changes in a referendum.

Among the ongoing concerns is the right of employees to work reasonable hours and to be entitled to a day off on Sundays.

Other issues include extra deliveries and traffic generated by the longer operating store hours.

“The unions will not be alone in the referendum fight,” Louis Schelbert, a member of the Green party from Lucerne, told the media.

A parliamentary commission is looking into a motion from the senate to allow shops across the country to open from 6am to 8 pm from Monday to Friday, and from 6 am until 7pm on Saturday.

The cantons would be able to adopt more liberal hours, under the proposal, spearheaded by Filippo Lombardi, a Christian Democrat from Ticino.

Fabio Abate, a Liberal senator from Ticino, meanwhile, wants to relax federal laws currently limiting Sunday shopping to tourist areas, main train stations and airports.

Geneva MP Christian Lüscher, sponsor of the motion for 24-hour gas station stores, said this would allow them to offer products and services meeting the needs of travellers at all times.

Ruedi Noser, a Liberal party member from Zurich, said the change would also address an anomaly in the operations of gas stations.

Current laws require them to close retail operations from 1 to 5 am from Mondays to Saturdays, as well as on Sundays.

However, staff can still sell fuel and food products from cafeterias.