Britain cannot be allowed access to the EU’s single market without accepting free movement of people, German Chancellor Angela Merkel said Thursday, warning she would not allow a free-for-all.

“If we don’t say full access to the internal market is linked to full freedom of movement, then a movement will spread in Europe where everyone just does whatever they want,” the chancellor told business leaders from the BDI industry federation.

Merkel urged German firms to back Berlin’s tough line on Brexit even in the face of potential economic harm, or risk undermining the European Union.

“We have to make our interests align so that European industry federations don’t put pressure on us” during talks with London, Merkel told the annual BDI gathering.

Some British politicians are confident that industry groups on the continent, fearful of losing their access to the UK, will push for a deal retaining Britain’s access to the EU single market while limiting migration across the Channel.