Sherrod Brown and 27 other U.S. senators Wednesday pledged not to intervene if the 340,000 unionized UPS workers go on strike.

The group of all Democrats, except independent Sen. Bernie Sanders of Vermont, also, according to a news release from Brown’s office, affirmed their support for “workers exercising their right to strike if an equitable collective bargaining agreement cannot be reached.”

The 28 senators Wednesday sent a letter to Teamsters President Sean O’Brien and UPS chief executive Carol Tome to encourage the sides to reach a contract agreement that gives workers “fair wages, safe working conditions, affordable health care and dignified retirement.”

“We understand that UPS Teamsters recently announced their overwhelming authorization of a strike — which would be the largest work stoppage at a single employer in American history — if the two parties cannot reach agreement on a contract by August 1. We are hopeful that both sides can negotiate in good faith and reach a consensus agreement that addresses basic human needs and allows workers to do their jobs safely and with dignity,” the letter states.

Pennsylvania Sens. Bob Casey and John Fetterman also signed the letter. An identical letter was signed by 171 House members.

Earlier this week, O’Brien asked the White House not to intervene if there is a strike. Negotiations have been at a standstill with a July 31 deadline for a new contract looming.

The union has threatened a strike if a deal is not reached by the time the collective bargaining agreement expires. Asked during a webcast with members Sunday on whether the White House could force a contract on the union, Teamsters President Sean O’Brien said he has asked the White House on numerous occasions to stay away.

The Teamsters represent more than half of the Atlanta-based company’s workforce in the largest private-sector contract in North America. If a strike does happen, it would be the first since a 15-day walkout by 185,000 workers crippled the company a quarter century ago.

Before contract talks broke down, both sides had reached tentative agreements on several issues, including installing air conditioning in more trucks and getting rid of a two-tier wage system for drivers who work weekends and earn less money. A sticking point in negotiations is wage increases for part-time workers, who make a minimum of $16.20 an hour, according to UPS.