Germany's powerful union IG Metall warned Sunday that metal workers will vote on major strike action if no agreement is reached this week in a wage dispute.
Nearly 400,000 workers have already joined a wave of shorter "warning strikes" in recent days, hitting big German companies including BMW, Siemens and Bosch.
"The IG Metall wants a quick deal, but on fair terms," the union's deputy leader Detlef Wetzel told Monday's edition of Bild daily, demanding employers raise their offer.
If no agreement is reached this week, "we will go to the ballot after Pentecost," he said, giving a May 21 deadline for a union vote on stepped up industrial action.
IG Metall is Europe's largest union with more than 2.2 million members. Pay talks in the metalworking sector are closely watched because they set the tone for other industries.
The union is demanding a 5.5-percent salary rise this year for 3.7 million metalworkers spread across different branches, from automobiles to electronics. Employers have offered a 2.3-percent rise over a slightly different timeframe.