If the changes are small, e.g. they ask employees to come in 15 minutes early, but they also leave 15 minutes early, then they can do this, without asking for consent.
If the changes are substantial, e.g. changing shifts or introducing shifts when previously there were none, decreasing or increasing working hours substantially, decreasing wages, then there are rules to follow, as outlined in the Statute for Employees, art. 41.
Basically, the employee has 3 choices:
A. Challenge the change
B. Request to dissolve the work contract (NOT the same as quitting!!)
C. Accept the change
The employer needs to communicate the proposed change in writing with at least 15 days notice, if the change affects an individual employee. If it’s a collective measure, then there needs to be a negotiation period of max. 15 days first, during which representatives of the employees will be informed about the necessity of the measure, and discuss how to possibly avoid or reduce negative consequences for the affected employees. A workers’ union can be involved at this stage as well, of course.
The employee then has 20 days as of receipt of the notice, to challenge the announced change. If the measure is not communicated in writing, it has to be done in another reliable way (e.g. verbally but with a witness present) and if it is not communicated at all before it takes effect, the employee has up to 12 months as of the date the change has taken place.
When challenged, the court can rule the change to be justified or unjustified, but even when ruled justified, if the employee doesn’t want to continue working under the new circumstances, they have the right to ask for the work contract to be dissolved within a window of 15 days after the ruling.
They need to put this request to the employer, but if they refuse, they have to go to court to get a ruling from a judge.
We recommend asking a specialist labour lawyer for help with each of the procedures outlined above, to make sure they are put forward correctly. Easiest access through a workers’ union, you don’t have to be a member to ask for their advice, but they might charge a small contribution. CCOO and UGT are large unions in Spain, with a listing of offices on their respective websites.
Link to article about employer’s decision to decrease working hours.
Link to article on the right to ask for adaptation work schedule to personal situation