Stripe different plans - ruby-on-rails

Question

So I got stripe up and running, however I have 3 different payment plans.
I'd like to capture what plan they clicked on, and use that to connect them to their right plan id.
This is what my form looks like:
<%= form_tag charges_path, id: "payment-form" do %>
<span class="payment-errors"></span>
<div class="form-row">
<label>
<span>Card Number</span>
<input type="text" size="20" data-stripe="number" maxlength="20" />
</label>
</div>
<div class="form-row">
<label>
<span>CVC</span>
<input type="text" size="4" data-stripe="cvc" maxlength="4"/>
</label>
</div>
<div class="form-row">
<label>
<span>Expiration (MM/YYYY)</span>
<input type="text" size="2" data-stripe="exp-month" maxlength="2"/>
</label>
<span> / </span>
<input type="text" size="4" data-stripe="exp-year" maxlength="4"/>
</div>
<button type="submit">Submit Payment</button>
<% end %>
I link to them like this:
<%= link_to 'Start Your Free Trial', new_charge_path(:plan_id => 1) %>
and the controller looks like this:
def create
customer = Stripe::Customer.create(
:email => 'exaimple#stripe.com',
:plan => plan_id,
:card => params[:stripeToken]
)
current_user.update_attributes(:stripe_customer_token => customer.id)
redirect_to root_url, notice: 'Successfully subscribed'
rescue Stripe::CardError => e
flash[:error] = e.message
redirect_to charges_path
end
which results in the error:
undefined local variable or method `plan_id'