The hard line from federation head Pierre-Yves Maillard reflects the Swiss government's struggle to forge domestic consensus on how or even whether to move ahead with the pact, which has run aground after nearly five years of negotiations.
"We will engage in this substantive debate by asserting that we want to maintain bilateral agreements (with the EU) but in a context of defence of wages, defence of our ability to decide on our measures to protect wages independently," Maillard told his group's annual news conference in the Swiss capital.
Any accord put before the Swiss people required a "marked social agenda", he said.
Making sure Switzerland can maintain the safeguards it imposed to protect Europe's highest wages from German plumbers, French electricians or Italian roofers on temporary assignment has become a main sticking point in bilateral ties.
Reservations about restricting the rights of EU citizens and state aid are also stumbling blocks in the talks, which have effectively been put on hold while Switzerland gears up for a referendum in May on whether to abolish an accord on the free movement of EU citizens.
Battling the referendum campaign is a priority for the Swiss government, which has struggled to put relations with the surrounding EU on a new footing.
Brussels wants the Swiss to endorse the treaty, which would have Bern routinely adopt single-market rules and create a more effective platform to resolve disputes.
The Swiss have dragged their feet for months, annoying Brussels and triggering a row over cross-border stock trading.
The treaty stalled amid opposition that spanned the normally pro-Europe centre left to the anti-EU far right. Critics say the pact infringes Swiss sovereignty to the extent that it would never get through parliament or pass a referendum.
Maillard, a member of parliament for the centre-left Social Democrats, a government coalition partner, also called on the Swiss National Bank to contribute some of its annual profit to shoring up the public pension scheme.
The central bank has opposed the idea, saying it needs all its foreign currency reserves to help tame the strength of the Swiss franc. It also uses negative interest rates and intervention on currency markets to rein in the franc.
"We think that given the volume of (SNB) reserves and the nature of these profits, which are linked to negative interest rates that harm pensions, it would be logical to redistribute part of them to the public pension system," Maillard told Reuters.
He did say how much the SNB should chip in. The central bank said on Thursday it expects a 2019 profit of 49 billion Swiss francs (38.66 billion pounds).
(Editing by Larry King)
By Stephanie Nebehay