Firms in former Communist countries pay much lower salaries, giving them a huge competitive edge when bidding for work overseas.
This attack came on Wednesday from the French President, Emmanuel Macron, in Salzburg (Austria). She then arrived in Bucharest, Romania today in a navy minidress and matching jacket to meet with President Klaus Iohannis and his wife Carmen.
Nine other former communist member states have also voiced their opposition, as has Denmark, which says the proposals don't go far enough to protect Danish collective bargaining.
While Hungary and Poland criticised the proposed European Union directive about workers posted overseas, labelling it protectionist, Slovakia is in agreement with France that the European Union needs a rule that workers posted overseas should earn salaries equal to those in the country they are working in. France wants to make 12 months the maximum period that a worker can be "posted".
They thus start with a huge competitive advantage when bidding for work overseas in wealthy countries - and do not contribute to the cost of maintaining the local social safety net.
Some labor market experts have argued that it's a mistake to just isolate posted workers.
France also demands greater efforts to fight fraudulent use of the directive, under which 286,000 people were employed in the country in 2015.
His first stop on Wednesday was Salzburg, Austria, where he met with Chancellor Christian Kern, the Czech Prime Minister Bohuslav Sobotka and Slovakia's Robert Fico.
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However, the Czech Republic and Slovakia want the field of road transport exempted from the EU's future directive.
An estimated 500,000 of its nationals are employed by Polish companies in other European Union members.
Poland is the country that benefits most from the Posted Workers Directive.
Franco-German unity is seen as a pre-requisite for an overhaul of the rule.
Pierre Vimont, a senior fellow at the Carnegie Europe think tank, called changing the directive "a symbolic case" for Macron whose popularity ratings have plummeted since he took office in May.
The 39-year-old centrist is pushing for a new mechanism to screen non-EU investments, particularly from China, into strategic areas of the European economy, as well as tougher measures to block the dumping of cheap imports on the continent. Macron's tour of the region is aimed at winning some understanding for the position of the more prosperous countries.
Last year, the European Commission proposed new rules to regulate pay for posted and local workers, but the proposals were opposed by member states in central and eastern Europe.