In a letter ahead of this week's EU summit, European Commission President Ursula von der Leyen calls for a joint pact against "over-implementation" - when countries go further in their legislation than what has been jointly agreed at EU level.
"A rule decided at EU level cannot be made more complicated when it is introduced or transposed into national law," von der Leyen writes, according to the Ansa news agency, among others.
However, the European Trade Union Confederation (ETUC) is threatening legal action if the pact is used to water down labour market regulations.
“Unless social and labour laws are exempted . . . important progress made by workers over the past 100 years risks being undermined,” Secretary-General Esther Lynch wrote in a statement.