The MTA’s largest workers union is calling for a temporary cease-fire in its ongoing contract war so it can help the agency renegotiate “toxic” swap deals with big banks that have cost it more than $100 million annually.

The Transport Workers Union Local 100 — extending an unprecedented olive branch to MTA managers — is offering to picket and boycott banks that won’t let the agency out of the deals, said President John Samuelsen.

“I would get the whole New York labor movement behind it,” said Samuelsen.

The MTA agreed to most of the swap deals before the economy crashed.

The agency didn’t respond to the union’s offer to boycott.