More than 37,000 people have signed a petition to thank coffee giant Starbucks for its equal marriage support after marriage opponents called for an international boycott.

Tens of thousands have signed the petition to thank Starbucks so far, compared with 6,200 who have said they will boycott the coffee shops as suggested by the National Organization for Marriage’s Dump Starbucks campaign.

When the petition reaches 40,000 signatures, the website SumofUs.org says it will deliver a giant ‘thank you’ card to the company’s Seattle headquarters and give executives “moral support to keep standing up for equality”.

The petition page says: “NOM is targeting Starbucks because the company recently stood up publicly to support gay marriage legislation in their home state of Washington in the United States. When it passed, the bill’s lead sponsor said that support from business convinced moderate legislators to vote for it. Without support from companies like Starbucks, the gay marriage law might have failed.”

In January, the coffee giant said it was “proud” to join other Washington-based employers like Microsoft and Nike in supporting the equal marriage in the state.

The state legislature voted in favour of equal marriage rights for gay couples in February.

Taren Stinebrickner-Kauffman, executive director for SumofUs.org said: “Starbucks customers are speaking loud and clear: Being for equality is good for business. We’re seeing almost unprecedented levels of interest from our members in this campaign. NOM is soon going to have to face the truth that it’s losing the culture war it’s been waging against LGBT people.”

The Dump Starbucks campaign asks coffee-drinkers to boycott the brand “because it has taken a corporate-wide position that the definition of marriage between one man and one woman should be eliminated and that same-sex marriage should become equally ‘normal’.”

The petition can be signed here.